slayer vs killer

slayer and killer both are nouns.

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

As nouns, slayer and killer are synonyms defined as:

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