not bad vs swell

not bad is not a noun while swell is a noun.

Word	Noun	Adjective	Verb	Adverb
not bad	No	Yes	No	No
swell	Yes	Yes	Yes	No

As adjectives, not bad and swell are synonyms defined as:

Other synonyms of not bad include bang-up, bully, corking, cracking, dandy, great, groovy, keen, neat, nifty, old, peachy, slap-up, smashing.

not bad (noun)	swell (noun)
	a crescendo followed by a decrescendo
	the undulating movement of the surface of the open sea
	a rounded elevation (especially one on an ocean floor)
	a man who is much concerned with his dress and appearance

not bad (adjective)	swell (adjective)
excellent	excellent

not bad (verb)	swell (verb)
	expand abnormally
	cause to become swollen
	increase in size, magnitude, number, or intensity
	come up, as of a liquid
	become filled with pride, arrogance, or anger
	come up (as of feelings and thoughts, or other ephemeral things)