hit man vs murderer

hit man and murderer both are nouns.

Word	Noun	Adjective	Verb	Adverb
hit man	Yes	No	No	No
murderer	Yes	No	No	No

As nouns, murderer is a hypernym of hit man; that is, murderer is a word with a broader meaning than hit man:

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

Other hypernyms of hit man include liquidator, manslayer.

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