diacritic vs circumflex

diacritic and circumflex both are nouns.

Word	Noun	Adjective	Verb	Adverb
diacritic	Yes	Yes	No	No
circumflex	Yes	No	No	No

As nouns, circumflex is a hyponym of diacritic; that is, circumflex is a word with a more specific, narrower meaning than diacritic:

diacritic: a mark added to a letter to indicate a special pronunciation
circumflex: a diacritical mark (^) placed above a vowel in some languages to indicate a special phonetic quality

Other hyponyms of diacritic include accent, accent mark, breve, cedilla, hacek, wedge, macron, tilde, umlaut, diaeresis, dieresis.

diacritic (noun)	circumflex (noun)
a mark added to a letter to indicate a special pronunciation	a diacritical mark (^) placed above a vowel in some languages to indicate a special phonetic quality

diacritic (adjective)	circumflex (adjective)
capable of distinguishing