What is the meaning of Cutthroat?

A murderer who slits the throats of victims.

An unscrupulous, ruthless or unethical person.

A three-player pocket billiards game where the object is to be the last player with at least one ball still on the table.

Involving the cutting of throats.

Of or relating to a card game where everyone plays for him or herself rather than playing with a partner.

Ruthlessly competitive, dog-eat-dog.

Source: wiktionary.org