sing vs singing

sing is not a noun while singing is a noun.

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

sing (noun)	singing (noun)
	the act of singing vocal music
	disclosing information or giving evidence about another

sing (adjective)	singing (adjective)
	smooth and flowing

sing (verb)	singing (verb)
make a whining, ringing, or whistling sound
divulge confidential information or secrets
to make melodious sounds
produce tones with the voice
deliver by singing