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A small, circle-shaped device that keeps the shrapnel out of Tony Stark's (AKA Ironman) heart. It also powers his kickass suit.
He's also got one back home that used to power his factory, until he used it to blow his insane business partner, Obadiah Stane, to kingdom come.
James: Did you see that arc reactor, man?

Gary: The glowy thing in his chest?

James: Yeah!

Gary: Yeah, I want me one of those, man.
by The Deegemeister May 21, 2008
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