gunslinger vs manslayer

gunslinger and manslayer both are nouns.

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

As nouns, manslayer is a hypernym of gunslinger; that is, manslayer is a word with a broader meaning than gunslinger:

gunslinger: a professional killer who uses a gun
manslayer: a criminal who commits homicide (who performs the unlawful premeditated killing of another human being)

Other hypernyms of gunslinger include liquidator, murderer.

gunslinger (noun)	manslayer (noun)
a professional killer who uses a gun	a criminal who commits homicide (who performs the unlawful premeditated killing of another human being)