accent mark vs diacritic

accent mark and diacritic both are nouns.

Word	Noun	Adjective	Verb	Adverb
accent mark	Yes	No	No	No
diacritic	Yes	Yes	No	No

As nouns, diacritic is a hypernym of accent mark; that is, diacritic is a word with a broader meaning than accent mark:

accent mark: a diacritical mark used to indicate stress or placed above a vowel to indicate a special pronunciation
diacritic: a mark added to a letter to indicate a special pronunciation

Other hypernyms of accent mark include diacritical mark.

accent mark (noun)	diacritic (noun)
a diacritical mark used to indicate stress or placed above a vowel to indicate a special pronunciation	a mark added to a letter to indicate a special pronunciation

accent mark (adjective)	diacritic (adjective)
	capable of distinguishing