dressed to kill vs spiffed up

dressed to kill and spiffed up both are adjectives.

Word	Noun	Adjective	Verb	Adverb
dressed to kill	No	Yes	No	No
spiffed up	No	Yes	No	No

As adjectives, dressed to kill and spiffed up are synonyms defined as:

Other synonyms of dressed to kill include dolled up, dressed-up, dressed, dressed to the nines, spruced up, togged up.

dressed to kill (adjective)	spiffed up (adjective)
dressed in fancy or formal clothing	dressed in fancy or formal clothing