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A large, not-very-nice female black dragon in the MMORPG World of Warcraft. She is Nefarian's sister and daughter of Neltharion a.k.a. Deathwing (who first appeared in Warcraft II). One of the toughest raid bosses in the game to defeat.
PLAYER #1: "Let's get a group together to kill Onyxia."

PLAYER #2: "Fuck no, I'm scared of her!" (soils self)
by Rabid_Caterpillar July 12, 2006
One mean mother-fucker.
Onyxia is a big fat bitch! :(
by Matt April 02, 2005