[mule] n [ME, fr. OF mul, fr. L mulus] (13c) 1 a: a hybrid between a horse and a donkey; esp: the offspring of a male donkey and a mare b: a self-sterile plant whether hybrid or not c: a usu. 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 drugs
[2]mule n [MF, a kind of slipper, fr. L mulleus shoe worn by magistrates] (1562): a shoe or slipper without quarter or heel strap--compare scuff