antipope vs Vicar of Christ

antipope and Vicar of Christ both are nouns.

Word	Noun	Adjective	Verb	Adverb
antipope	Yes	No	No	No
Vicar of Christ	Yes	No	No	No

As nouns, Vicar of Christ is a hypernym of antipope; that is, Vicar of Christ is a word with a broader meaning than antipope:

antipope: someone who is elected pope in opposition to another person who is held to be canonically elected
Vicar of Christ: the head of the Roman Catholic Church

Other hypernyms of antipope include Bishop of Rome, Catholic Pope, Holy Father, pontiff, pope, Roman Catholic Pope.

antipope (noun)	Vicar of Christ (noun)
someone who is elected pope in opposition to another person who is held to be canonically elected	the head of the Roman Catholic Church