What is the X in X-mas?
1550s, "to cut thin shavings from (something) with a knife," from Middle English whittel "a knife" (c1400), variant of thwittle (late 14c.), from Old English þwitan "to cut," from Proto-Germanic *thwitanan (cf. Old Norse þveita "to hew"). Figurative sense is attested from 1746. Related: Whittled; whittling.