mule [OE] A mule results from crossing a donkey and a horse, strictly a male donkey and a female horse (the technical name for the offspring of a female donkey and a stallion is hinny [L17th] from Latin hinnus). Mules have traditionally been used as beasts of burden, and are also traditionally regarded as stubborn. Someone stubborn, stupid, or physically tough has been called a mule since the 15th century. As a name for a courier for illicit drugs, mule dates from the 1920s in US slang. The name of the animal goes back to Latin mulus. It has no connection with mule [LME] in the sense ‘a slipper or light shoe without a back’. This comes from a term for the reddish shoes worn by magistrates in ancient Rome, Latin mulleus calceus.