C clef vs clef

C clef and clef both are nouns.

Word	Noun	Adjective	Verb	Adverb
C clef	Yes	No	No	No
clef	Yes	No	No	No

As nouns, clef is a hypernym of C clef; that is, clef is a word with a broader meaning than C clef:

C clef: a movable clef that puts middle C on one of the lines of a staff
clef: a musical notation written on a staff indicating the pitch of the notes following it

C clef (noun)	clef (noun)
a movable clef that puts middle C on one of the lines of a staff	a musical notation written on a staff indicating the pitch of the notes following it