Still to this day no one has convinced me that fornication is explicitely condemned in the Bible. There is no escaping the fact that the definition of Porneai--according to Strong's concordance--vaguely means "sexually immoral"--mostly being associated with prostitution. How do we know that fornication is considered "sexually immoral"? It just pushes the question back a step. I know that in the Hebrew version of the Old Testament, the word did refer to fornication, but we don't use that, we go by the Septuagint--which, does not mention fornication as all as far as I am concerned.
If you're looking at Strong's, though it is not the most authoritative source, it indeed defines porneia as fornication, as do ALL the major lexicons and dictionaries.

Google might provide a crumb of comfort to those who prefer dissenting opinion, but the fact remains that such is extremely *marginal* and in opposition to a genuinely overwhelming scholarly consensus to the contrary.
I cannot help but remain completely unimpressed by what has passed for counterargument in this thread. If as the NT asserts our eternity might ride on avoiding or embracing porneia (references in Kittel below), given the scholarly consensus placing fornication firmly within its semantic domain, I would not personally wager my spiritual health or eternal destiny on a fringe alternative that finds representation in no major mainstream resource whatsoever.
When used, as it often is, in its literal sense (as opposed to figurative usage for things like spiritual idolatry) porneia can be used of more than fornication, but not less.
Opening multiple major lexicons in Bibleworks we also find porneia as fornication:

TDNT (F. Hauck and S. Schulz, “porneia,” in Gerhard Kittel, ed.,
Theological Dictionary of the New Testament, VI, pp. 579–595) also defines porneia as fornication:
"
The NT is characterized by an unconditional repudiation of all extra-marital and unnatural intercourse... the concrete directions of Paul bring to the attention of Gentile Christians the incompatibility of porneia and the kingdom of God (in the list of vices in Rom 1:24-32; 13:13; 1 Cor 5:10f.; 6:9f.; 2 Cor 12:20f.; Gal 5:19-21; Col 3:5, 8f.; cf. also Eph 4:25-31; 5:3f.; 1 Tim 1:9f.; 2 Tim 3:2-5). Porneia occurs 8 times; akatharsia 4 times, while in 5 instances he begins with porneia or sexual sins, cf. Juncker, 113-117 and Exc. "Lasterkataloge" in Ltzm. R. on 1:31). No pornos has any part in this kingdom: 1 Cor 6:9; Eph 5:5. In 1 Cor 6:9 the sexual vices (pornoi, moichoi, malakoi, arsenokoitai) are put next to the chief sin of idolatry... As individuals are to steer clear of porneia, so it is the apostle's supreme concern to keep the communities free from such sins, since toleration of the offender makes the whole church guilty and constitutes an eschaltological thread (1 Cor 5:1ff.; cf. Heb 12:14-16. Thus Paul demands that the congregation expel the impenitent wrong-doer (1 Cor 5:13) and break off all felowship with those who live licentious lives (5:9). 2 Cor 12:19-21 expresses a concern lest the impenitence of those who have committed fornication should make necessary his intervention in the affairs of the community. The porneia of individual members makes the whole church unclean and threatens the whole work of the apostle, which is to present pure communities to Christ, 2 Cor 11:2... God's mighty will for the salvation of men is hagiasmos, 1 Thess 4:3; cf. also Eph 5:3-5. This includes sanctification of the body too and thus excludes any acceptance of
fornication, 1 Thess 4:1-5... A man shames his own body by
fornication, 6:18 He also brings shame on the body of Christ. Licentiousness is one of the expressions of the sarx, Gal 5:19. It is totally opposed to the work of the Holy Spirit, Gal 5:22. It belongs to what is earthly (Col 3:5), whereas Christians should seek what is above (Col 3:1-3). Paul again and again mentions porneia alongside akatharsia, 2 Cor 12:21; Gal 5:19; Col 3:5; cf. also Eph 5:3-5). He realizes not every one has the gift of continence. As a protection against the evil of
fornication the man who does not have it should take the divinely prescribed way of a lawful marriage, 1 Cor 7:2. Severe though Paul's condemnation of
fornication may be, there is no doubt that for him it is forgiven through Christ like all other sins. Along the same lines as Paul Hebrews ascribes the salvation of Rahab the harlot to her faith (11:31), though James (2:25) takes another view and thinks she is justified by her works. Among the seven letters of Revelation that to Pergamon accuses the Nicolatians of leading the congregation astray by compromising with the cultural life of the surrounding world in the eating of meat sacrificed to idols and the practicing of free sexual intercourse (porneia), 2:14. For the author the OT model for this is the doctrine of Balaam who led Israel astray in the same fashion, Num 25:1ff; 31:16. Along the same lines the church of Thyatira is charged with tolerating a prophetess who teaches the same practices, 2:20f... Among the leading pagan sins to which men will cling in the last days despite all the divine judgments, Rev 9:21 mentions idolatry, murder, witchcraft, and theft, and along with these unrestricted sexual indulgence... E. The Post-Apostolic Fathers. Herm. m. 4.1 warns against porneia which is the result of carnal desire. Cf. also Did 3.3."
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similarly DNTT defines porneia as fornication (H. Reisser, “porneia,” in Colin Brown, ed., New International Dictionary of New Testament Theology, vol. 1.497–501:
OT
3. In later Jewish Rab. language zenut (porneia) is to be understood as including not only prostitution
and any kind of extra-marital intercourse (Pirqe Aboth 2:8) but all marriages between relatives forbidden by Rab. law (cf. SB II 729 f.). Incest (Test. Rub. 1.6; Test. Jud. 13, 6; cf. Lev 18:6-18) and all kinds of unnatural sexual intercourse (e.g. Test. Ben. 9.1) were viewed as
fornication (porneia). One who surrenders to it shows ultimately that he has broken with God (cf. Wis. 14:17f.) ...Correspondingly the Dead Sea Scrolls give frequent warnings against such
fornication (1QS 1:6; 4:10; CD 2:16; 4:17, 20).
NT
In the NT the main weight of the word-group (used in all 55 times, of which porneia alone accounts for 25) falls clearly in Paul (21 times, of which 1 Cor and 2 Cor account for 15) and in Rev (19 times). From this one realizes that the question of porneia comes up for discussion particularly in the confrontation with the Gk. world and in the context of final judgment (there again linked with a person's relationship with God)...
2. In the Pauline writings the word-group porne denotes any kind of illegitimate sexual intercourse... If the congregation does not separate from such unchaste persons, the whole church is endangered (5:9ff), and stands under God's judgment (see art. Destroy, olethros). Since gnostic dualism saw in corporeality something that decayed and perished, sexual needs relating to one's body could be freely and spontaneously expressed. Paul passionately resisted this outlook (1 Cor 6:9-20). The stomach is meant for food, but the human body is not meant for unchastity (6:13). Human existence cannot be dissected into two realities, a sarkik and a pneumatic (v. 15 ff.). From porneia as from eidolatria, idolatry, one must flee (6:18; 10:14), because pornea cannot be secularized in the way the Corinthians hold. It is rather as if a religious and demonic power is let loose in porneia: "It is manifestly a different spirit, a pneuma akatharton (Matt 10:1), a spirit that is incompatible and irreconcilable with Christ, which takes control of man in porneia (Iwand, op cit, p. 615). Because man does not have a soma (body) but is a soma (i.e. is conceived as an indivisible totality), he is either a member of the body of Christ with his total reality or equally totally linked to a porne (1 Cor 6:15-19; cf. Heb 12:16). Thus Paul has to keep on warning not only his congregation (1 Cor 7:2; 10:8), but also others (Gal 5:19; Eph 5:3; 1 Thess 4:3) specifically against porneia, and with the greatest urgency, because it effects the whole person."
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...and also TDOT defines zanah as fornication, which is born out by the LXX translation as porneia (S. Erlandsson, "Zanah," in G. Johannes Botterweck and Helmer Ringren, eds., Theological Dictionary of the Old Testament, vol. IV, p. 99ff. which explores variations of the root zny/win Heb, Aramaic dialects (Jewish Aramaic, Samaritan, Syriac, Mandean), as well as Arabic (zana) and Ethiopic, Akkadian, etc.):
Quote from: Erlandsson, Zanah/TDOT
"The ptcp. xonah or ishshah zonah designates a woman who has sexual intercourse with somebody with whom she does not have a formal covenant relationship.
Any sexual relationship of a woman outside the marriage bond or without a formal union is termed fornication. When there is already a formal union and the sexual association is formed outside of that union, sanah becomes synonymous with ni'eph, commit adultery (ni'eph being thus a narrower term than zanah... The laws regulate sexual behavior precisely. When sexual intercourse is initiated before a marriage contract has been sealed and neither of the parties is already married, the man must marry the woman and ay not divorce her (Dt 22:28f.) If a woman has a formal partner, i.e is betrothed or married, but nevertheless of her own free will has intercourse with another man, she must suffer capital punishment (Dt. 22:22-27). If a man has a sexual relationship with the wife of another man, he likewise must suffer capital punishment... All sexual intercourse is to be set within a formal relationship. If this view is applied to the relationship between Israel and Yahweh, it follows that all worship of God must take place within the formal relationship of the covenant, in accordance with the covenant precepts (mishpatim debharim) of Yahweh... When Num 25:1 states that Israel committed fornication with (zanah 'el) the daughters of Moab, it is because zanah here refers to apostasy from the covenant expressed in the form of intercourse with Moabite women..." S. Erlandsson, "Zanah," in G. Johannes Botterweck and Helmer Ringren, eds., Theological Dictionary of the Old Testament, vol. IV, pp. 99ff.
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...cf. also DPL (D. F. Wright, "Sexuality, Sexual Ethics" in Gerald F. Hawthorne, Ralph P. Martin, and Daniel Reid, eds.,
Dictionary of Paul and His Letters: A Compendium of Contemporary Scholarship (1993), pp. 871- 875):
"Paul never addressed the subject of human sexuality in a systematic manner, but said much about it in response to particular questions. Nevertheless, 1 Thessalonians 4:1–8 suggests that his basic teaching to a community of new converts covered sexual behavior. This was only to be expected in the Greco-Roman world where various forms of sexual license were common. Paul now reminds the Christians at Thessalonica that God’s will for their sanctification required abstinence from porneia (1 Thess 4:3, “sexual immorality” NIV). This Greek word and its cognates as used by Paul denote any kind of illegitimate—extramarital and unnatural—sexual intercourse or relationship...
3.2. Sex, Self and Christ. For Paul sexual intercourse is not on a par with the satisfying of other natural appetites like eating. To that extent his approach is as inimical to the post-Christian West’s obsession with unbridled sexual gratification as it was to Corinthian licentiousness. Sexual intercourse is uniquely expressive of our whole being. “All other sins a person commits are outside his body, but he who sins sexually sins against his own body” (1 Cor 6:18). To deal with a blatantly intolerable perversion of Christian freedom (unlike the subtler ascetic alternative), Paul applies his richly articulated concept of “body” (soma), which may mean—almost at one and the same time—a person’s physical nature (“the body is not meant for sexual license,” 1 Cor 6:13), the whole human self (“your bodies are members of Christ himself,” 1 Cor 6:15; “your body is a temple of the Holy Spirit,” 1 Cor 6:19) and the church as Christ’s body... Undergirding such teaching lies Paul’s distinctive anthropology, in which the flesh, or body, is no mere external expression or instrument of the true person that resides in some inner essence (see Psychology). For Paul it is truer to say that a human being is a body rather than has a body. In the Corinthian context this is a way of speaking about a Christian both as a sexual being and as a being “in Christ,” a member of his church -body. Hence, when Paul declares porneia to be uniquely a sin against our own body (1 Cor 6:18), he is not referring merely to the misuse of our sexual organs. Nor is he distinguishing sexual sins on the grounds that drunkenness or gluttony, for example, involve things outside the body—drink and food in this case. He may be picking up a notion advanced by some libertine Corinthians, that nothing one does sexually or physically can touch the inner citadel of the soul. (Such sentiments are found among later Christian gnostics.) For Paul nothing could be further from the truth. Because sexual activity embodies the whole person, sinful union with a prostitute—or adultery or other extramarital intercourse—desecrates a Christian’s bodily union with Christ. “The association between Christ and the believer is regarded as just as close and physical as that between the two partners in the sex act” (Schweizer, 1065).
3.3. Sex in Relationship. Paul cites Genesis 2:24 (“the two will become one flesh”) to demonstrate what is involved in the seemingly casual one-night stand with another woman; you become one body with her (1 Cor 6:16; note that Paul substitutes his own favorite soma for the Septuagint’s sarx. It is the peculiar dignity of the one-flesh union of heterosexual marriage, on the other hand, that not only is it quite compatible with spiritual union with the Lord (1 Cor 6:17), but also it expresses the mysterion (“mystery”) of the union between Christ and his church (Eph 5:31–32; 2 Cor 11:2). The analogy covers not merely reciprocal mutual love, respect and care but the union itself... But if 1 Corinthians 6 responds to an antinomian “permissiveness” current in Corinthian Christianity, 1 Corinthians 7 deals with issues reflecting a more ascetic streak. At the outset Paul cites a statement from the Corinthians’ letter (so most commentators agree), “It is good for a man not to touch a woman” (1 Cor 7:1; NIV margin, “not to have sexual relations with.” See Col 2:21–23 for a possible parallel). The teaching this evokes from Paul is concerned solely with marriage and sexual relations within marriage. The assertion Paul quotes almost certainly expresses the conviction of some Corinthian Christians that sexual activity between male and female, even if married (hence NIV’s rendering “good ... not to marry,” 1 Cor 7:1, is misleading), had no place in the Christian’s life. (Perhaps teaching such as 1 Cor 6:15–16 had been misunderstood as warranting this conclusion. See also 1 Tim 4:1–5 for a reaffirmation of God’s good creation of marriage.) The fact that Paul proceeds to speak only about marriage is highly significant: for him there is no acceptable context for sex except within marriage. Yet the issue is not marriage as such but sexual intercourse—or perhaps better still, marriage as inseparably entailing sexual relations... Marriage (i.e., monogamy) is needed and right because porneia as an outlet for sexuality is intolerable (1 Cor 7:2). The implication is clear: the satisfying of sexual desires is not wrong, and marriage is its appointed setting. (The parallels with 1 Thess 4:3–5 exclude the reduction of marriage to merely a cover for uncontrolled sexual gratification.) Moreover, sex is not a dispensable dimension of marriage; like responsible love and respect (cf. above on Eph 5), it is one of the mutual obligations of husband to wife and wife to husband (1 Cor 7:3). For within marriage neither partner retains sole ownership of his or her own body (1 Cor 7:4). Sex within marriage must exemplify what Paul teaches later in 1 Corinthians: “In the Lord, however, woman is not independent of man, nor is man independent of woman” (1 Cor 11:11; see Man and Woman).
3.5. A Place for Abstinence. From the perspective established by Paul in 1 Corinthians 7:2–4, the issue is no longer “is sex (within marriage) ever good?” but “when, if ever, is abstinence from sex within marriage right?” Paul sets out three criteria: (1) mutual consent, (2) for a limited time only, and (3) for religious purposes (1 Cor 7:5). And even this provision for abstinence is a concession—for verse 7 (Paul’s recognition that singleness—involving abstinence—is possible by divine gift alone) suggests that the “concession” of verse 6 refers to verse 5, and not to verse 2–4. The underlying assumption is that by divine appointment marriage and sexual relations go together, as do singleness and abstinence from sex; what God has joined together, humans should not separate. Hence the concessionary character of verse 5, perhaps with the Corinthian ascetics particularly in mind.
The teaching of this chapter so far obviously disallows an understanding of sexual intercourse as intended solely for procreation. Even if artificial means of contraception are not in view, the accent falls unambiguously on sexual relations as expressive of selfless mutuality between married partners, of their belonging in the Lord to each other, not to him- or herself.
1 Corinthians 7:8–9 adds little to the picture painted so far. For reasons that Paul will spell out later, at 1 Corinthians 7:29–35, his preference is for the unmarried and widowed to remain so, like himself. But for those who lack the charisma of sex-free singleness, it is much better to marry than be consumed with inward desire—even, it seems, if that desire is controlled and not given vent in porneia
4. Conclusions.
The prevalent sexual license of Western society makes Paul’s teaching both peculiarly relevant—for it was addressed to Christians in a world in this respect not too dissimilar to ours—and painfully sharp. He allows no compromise of the restriction of sexual activity to (heterosexual) monogamous marriage. Such an ethic must seem almost utopian to our sex-besotted age, in which it appears at times that one’s identity is made to reside in one’s sexual organs and their untrammeled exercise. Paul espouses an altogether higher view of sex that could never allow it to be casual or promiscuous, simply because it is an act uniquely expressive of one’s whole being. From a Pauline perspective a cavalier freedom in sexual behavior can be bought only at the cost of trivializing the human person. His emphasis on mutuality, including sexual mutuality, within marriage—so marked an advance on the practice and precept of contemporary Hellenism and Judaism —is attractive in a day of increasing sexual violence and exaggerated insistence on individual sexual rights.
And if for Paul the eschatological urgency accentuated the advantages in remaining unmarried—but only with God’s enabling charisma —he provides an example of a teacher on sexuality sensitive to differences of circumstances and persons. If his situation heightened the note of sexual discipline, it is arguable that it was in every way healthier—spiritually, psychologically, physically—than alternatives offered and promoted today."
I've seen a lot of places where translators pick "fornication" more out of a desire to put forth their personal beliefs than out of a desire to be as faithful as possible to the original language.
It's easy to assert something like this with no actual demonstration or evidence. Perhaps instead translators use the word fornication for porneia because every major scholarly resource places it within the semantic domain of porneia.