sing vs quaver

sing is not a noun while quaver is a noun.

Word	Noun	Adjective	Verb	Adverb
sing	No	No	Yes	No
quaver	Yes	No	Yes	No

As verbs, quaver is a hyponym of sing; that is, quaver is a word with a more specific, narrower meaning than sing:

sing: produce tones with the voice
quaver: sing or play with trills, alternating with the half note above or below

sing (noun)	quaver (noun)
	a musical note having the time value of an eighth of a whole note
	a tremulous sound

sing (verb)	quaver (verb)
make a whining, ringing, or whistling sound	sing or play with trills, alternating with the half note above or below
divulge confidential information or secrets	give off unsteady sounds, alternating in amplitude or frequency
to make melodious sounds
produce tones with the voice
deliver by singing