Antichrist comes from the Greek Antichristos. In composition anti has different meanings: antibasileus denotes a king who fills an interregnum; antistrategos, a propraetor; anthoupatos, a proconsul; in Homer antitheos denotes one resembling a god in power and beauty, while in other works it stands for a hostile god. Following mere analogy one might interpret antichristos as denoting one resembling Christ in appearance and power; but it is safer to define the word according to its biblical and ecclesiastical usage.
The roots of the Antichrist idea go back to the Bible. In fact, in a sense they go back to the Old Testament and the Book of Daniel. And they're reinforced by certain passages in St. Paul, in the New Testament, and greatly elaborated down the centuries, including quite early in the Middle Ages.