noun

1. the offspring of a donkey and a horse; esp., the offspring of a jackass and a mare: mules are nearly always sterile
2. a small tractor or electric engine used to tow boats along a canal or move mine cars
3. a machine for drawing and spinning cotton fibers into yarn and winding the yarn on spindles
4. a hybrid animal, as the offspring of a canary and some other finch; esp., a sterile hybrid
5. Informal a stubborn person
6. Slang a person who smuggles drugs or narcotics into a country

Etymology: OFr, fem. of mul < L mulus, mule

noun

Etymology: Fr, ult. < L mulleus, red or purple shoe < IE base *mel-, dark-colored > Gr melas, black