killer vs slayer

killer and slayer both are nouns.

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

As nouns, killer and slayer are synonyms defined as:

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