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.

Short for cutthroat compound (an agentive-instrumental verb-noun compound word).

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