hired gun vs triggerman

hired gun and triggerman both are nouns.

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

As nouns, hired gun and triggerman are synonyms defined as:

Other synonyms of hired gun include gun, gun for hire, gunman, gunslinger, hit man, hitman, shooter, torpedo.

hired gun (noun)	triggerman (noun)
a professional killer who uses a gun	a professional killer who uses a gun