Merriam-Webster Collegiate Dictionary - mule

 I. noun  Etymology: Middle English, from Anglo-French mul, from Latin mulus  Date: 13th century  1.  a. a hybrid between a horse and a donkey; especially the offspring of a male donkey and a mare  b. a self-sterile plant whether hybrid or not  c. a usually sterile hybrid  2. a very stubborn person  3. a machine for simultaneously drawing and twisting fiber into yarn or thread and winding it into cops  4. slang a person who smuggles or delivers illicit substances (as drugs)  II. noun  Etymology: Middle French, a kind of slipper, from Latin mulleus shoe worn by magistrates  Date: 1562 a shoe or slipper without quarter or heel strap — compare scuff