Thomas the Apostle (called Didymus which means "the twin") was one of the Twelve Apostles of Jesus Christhttps://en.wikipedia.org/wiki/Thomas_the_Apostle
In the Book of Thomas the Contender [ circa 2nd c. AD], part of the Nag Hammadi, it is said to be Jesus himself: "Now, since it has been said that you are my twin and true companion, examine yourself…"
The apocryphal Acts of Thomas, written in the early third century, identifies him as "Judas Thomas", and fourth century historian Eusebius refers to him once as "Judas, who was also called Thomas".
- Judea had long been part of the Seleucid Empire, and a very common Macedonian name was Ptolemy, which, in Aramaic, was rendered as Talmai or Talmais. That might explain why he was also known as Judas , which basically identified him as Judean; because there was a desire to make it clear that he was of Judaic rather than Greek descent. Note that Bartholomew, the name of the Apostle who may have traveled to India with Thomas after Jesus' crucifixion, is believed to derive from bar Talmai, meaning "son of Ptolemy".
In Aramaic, the name "Thomas" is "Tauma." In Aramaic, the word for "Twin" is "Taama." Tauma was also known as Taama. In Aramaic, "Tauma who was called Taama" will become "Thomas who was called Didymus" in Greek losing the wordplay and the meaning becomes more obscure.
This explanation depends on the later texts that identify him as Judas Thomas, so it has not won much support.
Notes on the Catalogues of the Apostles in Matthew 10:3, Mark 3:18, Luke 6:15, in all of which he is coupled with Matthew, whose twin-brother he possibly was; and in Acts 1:13, where he is coupled with Philip. The name belonged probably to his childhood, and we are wholly without the knowledge which can explain it. The various theories which attempt to do so, from the statement of the Apostolical Constitutions that he had a twin sister Lydia, to the view that the name was given by our Lord to signify his double or halting spiritual nature, are never more than, and are sometimes much less than, elaborate guesses
If Thomas is stiff and obstinate in his incredulity, he is also stiff and obstinate in his affection and allegiance. “In him the twins, unbelief and faith, were contending with one another for mastery, as Esau and Jacob in Rebecca’s womb.”
In all probability he was a twin, possibly of S. Matthew, with whom he is coupled in all three lists of the Apostles in the Gospels: in the Acts he is coupled with S. Philip. That S. Thomas received his name from Christ (as Simon was called Peter, and the sons of Zebedee Boanerges) in consequence of his character, is pure conjecture. But the coincidence between the name and his twin-mindedness (James 1:8 [Such a [hypothetical] person is double-minded and unstable in all they do.]; James 4: is remarkable.
Peter got his name from Jesus for a spiritual reason. It's easy to think Jesus also gave Thomas this new name as a play on words (Tauma v Taama) based on dual mindedness - Thomas ended up being very doubtful and then strongly faithful in John 21.
John translated Didymus into Greek for the reader. Tauma (Ptolemy) was his name, while Taama (Twin / Didymus) was his nickname based on his name Tauma.
Judas was said by Eusebius to be Thomas' other name, but that was centuries later, like the Acts of Thomas was.
The additional names "Judas" and "Didymus" have causd further confusion in apocryphal literature in regard to Thomas, and have led to his identification with Judas of James, and hence, with Thaddaeus (see THADDAEUS), and also with Judas the brother of Jesus (compare Matthew 13:55 [Is this not the carpenter’s son? Isn’t His mother’s name Mary, and aren’t His brothers James, Joseph, Simon, and Judas?]). Thus in the "Acts of Thomas" he is twice called the "twin brother of the Messiah."
James the Just was also known as Jesus' brother.
It sounds like Jude/Judas (not Judas Iscariot) was another brother. It's not clear that this was Thomas.http://biblehub.com/topical/t/thomas.htm
Anyway, I don't think the apostles would have been confusing Jesus with Thomas even if they were twins, since they lived with Jesus for 3 years and Thomas is said to have touched the risen Jesus.