strip down vs undress

strip down is not a noun while undress is a noun.

Word	Noun	Adjective	Verb	Adverb
strip down	No	No	Yes	No
undress	Yes	No	Yes	No

As verbs, strip down and undress are synonyms defined as:

Other synonyms of strip down include discase, disrobe, peel, strip, uncase, unclothe.

strip down (noun)	undress (noun)
	partial or complete nakedness

strip down (verb)	undress (verb)
get undressed	get undressed
	remove (someone's or one's own) clothes