hit man

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A man hired by a crime syndicate as a professional killer.
• noun A hatchet man.

from the GNU version of the Collaborative International Dictionary of English.

• noun colloq. A professional murderer, esp. one working for a criminal organization; also called torpedo.
• noun A slanderer working for political purposes to damage the reputation of an opponent; a hatchet man.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Someone who kills for a living; a hired assassin

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a professional killer who uses a gun
• noun a professional killer who uses a gun