mule

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A backless slipper or shoe, often with a closed toe.
• noun The sterile hybrid offspring of a male donkey and a female horse, characterized by long ears and a short mane.
• noun A sterile hybrid, as between a canary and other birds or between certain plants.
• noun Informal A stubborn person.
• noun A spinning machine that makes thread or yarn from fibers.
• noun A small, usually electric tractor or locomotive used for hauling over short distances.
• noun Slang A person who serves as a courier of illegal drugs.

from The Century Dictionary.

• noun A hybrid animal generated between the ass and the horse.
• noun A hybrid in general; a mongrel; a cross between different animals.
• noun The scaup-duck, Fuligula marila. Rev. C. Swainson. [Prov. Eng.]
• noun In botany, a plant or vegetable produced by impregnating the pistil of one species with the fecundating element of another; a hybrid.
• noun In spinning, a machine invented by Samuel Crompton (completed 1779), in which the rovings are delivered from a series of sets of drawing-rollers to spindles placed on a carriage which travels away from the rollers while the thread is being twisted, and returns toward the rollers while the thread is being wound: so named because it was a combination of the drawing-rollers of Arkwright and the jenny of Hargreaves.
• noun In numismatics, a coin, token, or medal which, owing to mistake or caprice, consists of two obverse or two reverse types, or of which the obverse and reverse types are accidentally associated.
• noun A slipper without heel-piece or quarter.
• noun The foot of a wine-glass.
• noun A disease in horses.
• noun In mech., a locomotive for towing canal-boats, operated by compressed air, electricity, or steam: so called because it replaces the mules usually used for towing.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) A hybrid animal; specifically, one generated between an ass and a mare. Sometimes the term is applied to the offspring of a horse and a she-ass, but that hybrid is more properly termed a hinny. See hinny.
• noun (Bot.) A plant or vegetable produced by impregnating the pistil of one species with the pollen or fecundating dust of another; -- called also hybrid.
• noun A very stubborn person.
• noun A machine, used in factories, for spinning cotton, wool, etc., into yarn or thread and winding it into cops; -- called also jenny and mule-jenny.
• noun A slipper that has no fitting around the heel.
• noun (Zoöl.) a long-eared armadillo (Tatusia hybrida), native of Buenos Ayres; -- called also mulita. See Illust. under Armadillo.
• noun (Zoöl.) a large deer (Cervus macrotis syn. Cariacus macrotis) of the Western United States. The name refers to its long ears.
• noun (Mach.) an idle pulley for guiding a belt which transmits motion between shafts that are not parallel.
• noun cotton yarn in cops, as spun on a mule; -- in distinction from yarn spun on a throstle frame.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A shoe that has no fitting or strap around the heel, but which covers the foot.
• noun A generally sterile male or female hybrid offspring of a male donkey and a female horse.
• noun A generally sterile hybrid offspring of any two species of animals.
• noun informal A stubborn person.
• noun slang A person paid to smuggle drugs.
• noun numismatics A coin or medal minted with obverse and reverse designs not normally seen on the same piece, either intentionally or in error.
• noun gaming A character on an MMORPG used mainly to store extra inventory of the owner's primary character.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a slipper that has no fitting around the heel
• noun hybrid offspring of a male donkey and a female horse; usually sterile