circumflex vs diacritical mark

circumflex and diacritical mark both are nouns.

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

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

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

Other hypernyms of circumflex include diacritic.

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