What is the X in X-mas?
early 15c., "catapult, military engine for throwing large stones," from Middle French bombarde "mortar, catapult" (14c.), from bombe (see bomb (n.)). The same word, from the same source, was used in English and French late 14c. in reference to the bass shawm, a bassoon-like musical instrument, preserving the "buzzing" sense in the Latin.
1590s, from French bombarder, from bombarde "mortar, catapult" (see bombard (n.)). Figurative sense by 1765. Related: Bombarded; bombarding.