What is the X in X-mas?
early 14c., dasen, perhaps from Old Norse *dasa (cf. dasask "to become weary," with reflexive suffix -sk). Or perhaps from Middle Dutch dasen "act silly." Perhaps originally "to make weary with cold," which is the sense of Icelandic dasask (from the Old Norse word). Related: Dazed.
"a dazed condition," 1825, from daze (v.).