cut·throat 
(kŭtthrōt′)
(kŭtthrōt′)n.
1. A murderer, especially one who cuts throats.
2. An unprincipled, ruthless person.
3. A cutthroat trout.
adj.
1. Cruel; murderous.
2. Relentless or merciless in competition: a cutthroat business.
3. Sports & Games Being a form of a game in which each of three or more players acts and scores individually: cutthroat handball; cutthroat bridge.