slick up vs spiff up

slick up and spiff up both are verbs.

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

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

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

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