What is the X in X-mas?
c.1300, probably shortened from Old English geþrang "crowd, tumult" (related to verb þringan "to push, crowd, press"), from Proto-Germanic *thrangan (cf. Old Norse þröng, Dutch drang, German Drang "crowd, throng").
"go in a crowd," 1530s, from throng (n.). Related: Thronged; thronging.