antipope vs Holy Father

antipope and Holy Father both are nouns.

Word	Noun	Adjective	Verb	Adverb
antipope	Yes	No	No	No
Holy Father	Yes	No	No	No

As nouns, Holy Father is a hypernym of antipope; that is, Holy Father 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
Holy Father: the head of the Roman Catholic Church

Other hypernyms of antipope include Bishop of Rome, Catholic Pope, pontiff, pope, Roman Catholic Pope, Vicar of Christ.

antipope (noun)	Holy Father (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