What is the X in X-mas?
heavenly hall in which Odin receives the souls of heroes slain in battle, 1768, from Old Norse Valhöll "hall of the battle-slain;" first element from valr "those slain in battle," from Proto-Germanic *walaz (cf. Old English wæl "slaughter, bodies of the slain," Old High German wal "battlefield, slaughter"), from PIE root *wele- "to strike, wound" (cf. Avestan vareta- "seized, prisoner," Latin veles "ghosts of the dead," Old Irish fuil "blood," Welsh gwel "wound"). Second element is from höll "hall," from PIE root *kel- "to conceal" (see cell). Reintroduced by 18c. antiquaries. Figurative sense is from 1845.