killer vs manslayer

killer and manslayer both are nouns.

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

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

killer: someone who causes the death of a person or animal
manslayer: a criminal who commits homicide (who performs the unlawful premeditated killing of another human being)

killer (noun)	manslayer (noun)
predatory black-and-white toothed whale with large dorsal fin; common in cold seas	a criminal who commits homicide (who performs the unlawful premeditated killing of another human being)
a difficulty that is hard to deal with
someone who causes the death of a person or animal
the causal agent resulting in death