What is the X in X-mas?
Old English twin "double thread," from Proto-Germanic *twizna- (cf. Dutch twijn, Low German twern, German zwirn "twine, thread"), from the same root as twin (q.v.). The verb meaning "to twist strands together to form twine" is recorded from late 13c.; sense of "to twist around something" (as twine does) is recorded from c.1300. Related: Twined; twining.