spiff up vs slick up

spiff up and slick up both are verbs.

Word	Noun	Adjective	Verb	Adverb
spiff up	No	No	Yes	No
slick up	No	No	Yes	No

As verbs, spiff up and slick up are synonyms defined as:

Other synonyms of spiff up include smarten up, spruce, spruce up, titivate, tittivate.

spiff up (verb)	slick up (verb)
make neat, smart, or trim	dress and groom with particular care, as for a special occasion
	make neat, smart, or trim