Pronunciation: (but'uk),[key] —n. 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.