Keep Them Honest
To call at the end of a hand to prevent someone from bluffing.

Key Card
A card that gives a player a hand..  

Key Hand
In a session or tournament, the one hand that ends up being a turning point for the player, either for better or worse.

Kick It
To raise.  

Kicker
The highest unpaired card in your hand that doesn't participate in a straight or flush. Kicker is the card that does not contribute to the strength of your hand except by itself. Such cards can be vital in poker games with community cards to get your opponent out of the game.

Kill
A game is one in which a player may place an extra bet, causing the betting limits to go up for just that hand. It is a forced bet by a player who has just won the pot.

Kill Pot
Pot in the kill game is called kill pot.