hacek vs diacritical mark

hacek and diacritical mark both are nouns.

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

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

hacek: a diacritical mark (an inverted circumflex) placed above certain letters (such as the letter c) to indicate pronunciation
diacritical mark: a mark added to a letter to indicate a special pronunciation

Other hypernyms of hacek include diacritic.

hacek (noun)	diacritical mark (noun)
a diacritical mark (an inverted circumflex) placed above certain letters (such as the letter c) to indicate pronunciation	a mark added to a letter to indicate a special pronunciation