What is the X in X-mas?
"offspring of donkey and horse," from Old English mul, Old French mul "mule, hinny" (12c., fem. mule), both from Latin mulus (fem. mula) "a mule," probably from a pre-Latin Mediterranean language.
The mule combines the strength of the horse with the endurance and surefootedness of the ass, and is extensively bred for certain employments for which it is more suited than either; it is ordinarily incapable of procreation. With no good grounds, the mule is a proverbial type of obstinacy. [OED]Properly, the offspring of a he-ass and a mare; that of a she-ass and a stallion is technically a hinny. Used allusively of hybrids and things of mixed nature. As a type of spinning machine, attested from 1797 (so called because a hybrid of distinct warp and woof machines). Meaning "obstinate, stupid, or stubborn person" is from 1470s; that of "narcotics smuggler or courier" first attested 1935.
"loose slipper," 1560s, from Middle French mule, from Latin mulleus calceus "red high-soled shoe," worn by Roman patricians, from mullus "red" (see mullet (n.1)). Related: Mules.
: Sometimes they mule it in small amounts/ otherwise law-abiding countrymen into performing muling favors
(Heb. pered), so called from the quick step of the animal or its power of carrying loads. It is not probable that the Hebrews bred mules, as this was strictly forbidden in the law (Lev. 19:19), although their use was not forbidden. We find them in common use even by kings and nobles (2 Sam. 18:9; 1 Kings 1:33; 2 Kings 5:17; Ps. 32:9). They are not mentioned, however, till the time of David, for the word rendered "mules" (R.V. correctly, "hot springs") in Gen. 36:24 (yemim) properly denotes the warm springs of Callirhoe, on the eastern shore of the Dead Sea. In David's reign they became very common (2 Sam. 13:29; 1 Kings 10:25). Mules are not mentioned in the New Testament. Perhaps they had by that time ceased to be used in Palestine.