Don't have an Ieratikon or a Liturgikon with me, but I certainly don't recall any official liturgical book using the word "host." All rubrics I have seen usually call it the "Lamb" (amnos), or sometimes the "Holy Gifts," the "Holy Bread" or even less frequently just the "Bread" (artos).
These are all words that appear many times in the Proskomidi and in the rubrics of both the anaphora and the communion of the clergy (since it is necessary to distinguish between the two species -- and even necessary to distinguish the Lamb from the various other particles -- at that point). Once the Chalice is prepared for the laity, the rubrics just call it "Communion" and the priest, when he administers it, calls it the "Body and Blood of our Lord and God and Saviour, Jesus Christ."
Outside of liturgical books, I personally have never heard an Orthodox layperson or theologian call it the "host"... sounds very Anglo-Catholic to my ears, really, but I suppose it's a fine English word. It's not nearly as accurate as saying the "Lamb," though, since that's the specific part of the bread on the discos that is actually fractured, that a new ordinand is charged to guard, etc.