Pronunciation: (but'uk), [key]
1. Usually, buttocks.
a. (in humans) either of the two fleshy protuberances forming the lower and back part of the trunk.
b. (in animals) the rump.
2. Sometimes, buttocks. Naut.the aftermost portion of a hull above the water line and in front of the rudder, merging with the run below the water line.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.