'Antichrist' definitions:

Definition of 'Antichrist'

noun

(Christianity) the adversary of Christ (or Christianity) mentioned in the New Testament; the Antichrist will rule the world until overthrown by the Second Coming of Christ

Definition of 'antichrist'

From: Easton

Antichrist against Christ, or an opposition Christ, a rival Christ. The word is used only by the apostle John. Referring to false teachers, he says (1 John 2:18, 22; 4:3; 2 John 1:7), "Even now are there many antichrists."
This name has been applied to the "little horn" of the "king of fierce countenance" (Dan. 7:24, 25; 8:23-25).
It has been applied also to the "false Christs" spoken of by our Lord (Matt. 24:5, 23, 24).
To the "man of sin" described by Paul (2 Thess. 2:3, 4, 8-10).
And to the "beast from the sea" (Rev. 13:1; 17:1-18).

Definition of 'antichrist'

From: Hitchcock

Antichrist, an adversary to Christ