Attacking a mob in a MMORPGthat has already been engaged in combat. Usually for the purpose of obtaining looting rights over another individual or group.

Often a tactic used by a griefer to annoy other players.
You tried to kill-steal Peter Lee again, but failed miserably.

That guild of griefers keeps trying to kill-steal when we spawn mercs.
by camb November 18, 2003
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In online multiplayer games, when somebody else kills the enemy you are fighting. This often results in you earning less experience points than you normally would for killing that enemy because two people were attacking it.

Only noobs do this, and is considered a gamer's equivalent of a war crime among many.

"Dude, I was fighting a (insert enemy) and this noob came out of nowhere and stole my kill."
_ _ _

"Don't kill steal, asshole!"
by Big McHugeLarge January 7, 2008
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When you playing an online game that involves killing, and right when your about to kill someone, someone jumps out and kills him first
player 1: OHHH IMA KILL YOU
player 2: NOOOO
player 3: hahahah KILL STEAL!!
player 1: WTF U HAXZOR ROFLCOPTER ROFLCAKES!!!
by Slyslutter July 20, 2006
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a campaign to promote positive lifestyles for the youth and spread love and acceptance across the nation. myspace.com/stealkillanddestroy
Satan is going to Steal Kill and destroy you
by SKAD March 24, 2009
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