What is the X in X-mas?
Old English steda "stallion, stud horse," from Proto-Germanic *stodjon (cf. Old Norse stoð), from the root of Old English stod (see stud (2)). In Middle English, "a great horse" (as distinguished from a palfrey), "a spirited war horse." Obsolete from 16c. except in poetic, rhetorical, or jocular language.