smashing vs peachy

smashing is a noun but peachy is not a noun.

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

As adjectives, smashing and peachy are synonyms defined as:

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

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

smashing (adjective)	peachy (adjective)
excellent	of something resembling a peach in color
	excellent