overkiller
A word popular amongst people who play MUDs or other MMORPGS. To kill with an excessive amount of force usually in unfair Player VS Player fights.
In a Mud I use to play (called MUME) this was the most classic example:
Player1 attempts to fight Player2 in a fair fight. Player2 gets his ass kicked and calls for backup. Player1 gets trapped or Spam killed by Player2, Player3, Player4 and Player 5.