slap-up vs dandy

slap-up is not a noun while dandy is a noun.

Word	Noun	Adjective	Verb	Adverb
slap-up	No	Yes	No	No
dandy	Yes	Yes	No	No

As adjectives, slap-up and dandy are synonyms defined as:

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

slap-up (noun)	dandy (noun)
	a sailing vessel with two masts; a small mizzen is aft of the rudderpost
	a man who is much concerned with his dress and appearance

slap-up (adjective)	dandy (adjective)
excellent	excellent