triggerman vs hired gun

triggerman and hired gun both are nouns.

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

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

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

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