smashing vs groovy

smashing is a noun but groovy is not a noun.

Word	Noun	Adjective	Verb	Adverb
smashing	Yes	Yes	No	No
groovy	No	Yes	No	No

As adjectives, smashing and groovy are synonyms defined as:

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

smashing (noun)	groovy (noun)
the act of breaking something into small pieces

smashing (adjective)	groovy (adjective)
excellent	(British informal) very chic
	excellent