1
general::
1. A person, especially a professional killer, employed to kill someone, as in They thought the murder had been done by a hired gun. The noun gun has been slang for a professional criminal since the mid1800s. 2. A person with special knowledge or expertise who is employed to resolve a complex problem. For example, The legal team was looking for a hired gun to handle the antitrust angle of the case. [Slang; 1960s]
American Heritage Idioms