smashing vs old

smashing and old both are nouns.

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

As adjectives, smashing and old are synonyms defined as:

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

smashing (noun)	old (noun)
the act of breaking something into small pieces	past times

smashing (adjective)	old (adjective)
excellent	of long duration; not new
	(used especially of persons) having lived for a relatively long time or attained a specific age
	skilled through long experience
	(used for emphasis) very familiar
	excellent
	just preceding something else in time or order
	belonging to some prior time