accent mark vs diacritical mark

accent mark and diacritical mark both are nouns.

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

As nouns, diacritical mark is a hypernym of accent mark; that is, diacritical mark 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
diacritical mark: a mark added to a letter to indicate a special pronunciation

Other hypernyms of accent mark include diacritic.

accent mark (noun)	diacritical mark (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