tilde vs diacritical mark

tilde and diacritical mark both are nouns.

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

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

tilde: a diacritical mark (~) placed over the letter n in Spanish to indicate a palatal nasal sound or over a vowel in Portuguese to indicate nasalization
diacritical mark: a mark added to a letter to indicate a special pronunciation

Other hypernyms of tilde include diacritic.

tilde (noun)	diacritical mark (noun)
a diacritical mark (~) placed over the letter n in Spanish to indicate a palatal nasal sound or over a vowel in Portuguese to indicate nasalization	a mark added to a letter to indicate a special pronunciation