breve vs diacritical mark

breve and diacritical mark both are nouns.

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

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

breve: a diacritical mark (U-shaped) placed over a vowel to indicate a short sound
diacritical mark: a mark added to a letter to indicate a special pronunciation

Other hypernyms of breve include diacritic.

breve (noun)	diacritical mark (noun)
a diacritical mark (U-shaped) placed over a vowel to indicate a short sound	a mark added to a letter to indicate a special pronunciation