lady killer vs undoer

lady killer and undoer both are nouns.

Word	Noun	Adjective	Verb	Adverb
lady killer	Yes	No	No	No
undoer	Yes	No	No	No

As nouns, undoer is a hyponym of lady killer; that is, undoer is a word with a more specific, narrower meaning than lady killer:

lady killer (noun)	undoer (noun)
a man who takes advantage of women	a person who destroys or ruins or lays waste to
	a person who unfastens or unwraps or opens
	a seducer who ruins a woman