idolater vs infidel

idolater and infidel both are nouns.

Word	Noun	Adjective	Verb	Adverb
idolater	Yes	No	No	No
infidel	Yes	No	No	No

As nouns, infidel is a hypernym of idolater; that is, infidel is a word with a broader meaning than idolater:

Other hypernyms of idolater include gentile, heathen, pagan.

idolater (noun)	infidel (noun)
a person who worships idols	a person who does not acknowledge your god