mule

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The sterile hybrid offspring of a male donkey and a female horse, characterized by long ears and a short mane.
2. n. A sterile hybrid, as between a canary and other birds or between certain plants.
3. n. Informal A stubborn person.
4. n. A spinning machine that makes thread or yarn from fibers. Also called spinning mule.
5. n. A small, usually electric tractor or locomotive used for hauling over short distances.
6. n. Slang A person who serves as a courier of illegal drugs.
7. n. A slipper or shoe that has no counter or strap to fit around the heel.

Century Dictionary and Cyclopedia

1. n. A hybrid animal generated between the ass and the horse. The cross is usually between a jackass and a mare, that between a stallion and a she-ass being called a hinny. The mule is a valuable product of artificial selection, in some respects superior to either parent, and is extensively bred in America (Kentucky, Missouri, Mexico, etc.), in Spain, in Poitou (France), etc. It retains to some extent the specific characters of the ass, in the comparatively large head, long ears, roached mane, slim tail, and narrow, pointed hoofs, but acquires much of the size, strength, and symmetry of the mare. The animal matures slowly, is very long-lived, little liable to disease, and able to do more work than a horse under hard treatment and poor fare. Being also very agile and surefooted, it is serviceable as a pack-animal in countries where a horse could scarcely be used. The mule is not less docile and intelligent than the horse, and its strength is, in proportion to its size, probably greater. Mules are ordinarily incapable of procreation, and such seems to be always the case with the jack; but instances of impregnation of the hinny by the male ass or by a stallion are not rare.
2. n. A hybrid in general; a mongrel; a cross between different animals.
3. n. The scaup-duck, Fuligula marila. Rev. C. Swainson. [Prov. Eng.]
4. n. In botany, a plant or vegetable produced by impregnating the pistil of one species with the fecundating element of another; a hybrid.
5. n. 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.
6. n. 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. Thus, a denarius having a head of Tiberius on each side, or a denarius having the head of Tiberius on the obverse and a reverse type struck from one of the coin-dies of Augustus, would be a mule.
7. n. A slipper without heel-piece or quarter.
8. n. The foot of a wine-glass.
9. n. A disease in horses.
10. n. 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.

Wiktionary

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

GNU Webster's 1913

1. n. (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.
2. n. (Bot.) A plant or vegetable produced by impregnating the pistil of one species with the pollen or fecundating dust of another; -- called also hybrid.
3. n. A very stubborn person.
4. n. 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.
5. n. A slipper that has no fitting around the heel.

WordNet 3.0

1. n. a slipper that has no fitting around the heel
2. n. hybrid offspring of a male donkey and a female horse; usually sterile