killer vs doer

killer and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
killer	Yes	No	No	No
doer	Yes	No	No	No

As nouns, doer is a hypernym of killer; that is, doer is a word with a broader meaning than killer:

Other hypernyms of killer include actor, worker.

killer (noun)	doer (noun)
predatory black-and-white toothed whale with large dorsal fin; common in cold seas	a person who acts and gets things done
a difficulty that is hard to deal with
someone who causes the death of a person or animal
the causal agent resulting in death