sing vs warble

sing is not a noun while warble is a noun.

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

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

sing (noun)	warble (noun)
	a lumpy abscess under the hide of domestic mammals caused by larvae of a botfly or warble fly

sing (verb)	warble (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	sing by changing register; sing by yodeling
to make melodious sounds
produce tones with the voice
deliver by singing