hired gun vs liquidator

hired gun and liquidator both are nouns.

Word	Noun	Adjective	Verb	Adverb
hired gun	Yes	No	No	No
liquidator	Yes	No	No	No

As nouns, liquidator is a hypernym of hired gun; that is, liquidator is a word with a broader meaning than hired gun:

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

Other hypernyms of hired gun include manslayer, murderer.

hired gun (noun)	liquidator (noun)
a professional killer who uses a gun	(law) a person (usually appointed by a court of law) who liquidates assets or preserves them for the benefit of affected parties
	a criminal who commits homicide (who performs the unlawful premeditated killing of another human being)