grave accent vs accent mark

grave accent and accent mark both are nouns.

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

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

grave accent: a mark (`) placed above a vowel to indicate pronunciation
accent mark: a diacritical mark used to indicate stress or placed above a vowel to indicate a special pronunciation

Other hypernyms of grave accent include accent.

grave accent (noun)	accent mark (noun)
a mark (`) placed above a vowel to indicate pronunciation	a diacritical mark used to indicate stress or placed above a vowel to indicate a special pronunciation