See Definition for pseudochristos { [G5580]}
See Definition for antichristos { [G500]}
pseudochristos means a false Christ, a pretended Messiah, who
sets himself up instead of Christ, proclaiming that he is Christ.
Some have given about the same meaning to antichristos. But it is
much more probable that it means one diametrically opposed to Christ,
one who sets himself up against Christ, proclaiming that there is no
Christ.