dressed to kill vs dressed to the nines

dressed to kill and dressed to the nines both are adjectives.

Word	Noun	Adjective	Verb	Adverb
dressed to kill	No	Yes	No	No
dressed to the nines	No	Yes	No	No

As adjectives, dressed to kill and dressed to the nines are synonyms defined as:

dressed to kill and dressed to the nines: dressed in fancy or formal clothing

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

dressed to kill (adjective)	dressed to the nines (adjective)
dressed in fancy or formal clothing	dressed in fancy or formal clothing