What is the X in X-mas?
mid-13c., from a Scandinavian source akin to Old Norse rannsaka "to pillage," literally "search the house" (especially legally, for stolen goods), from rann "house," from Proto-Germanic *rasnan (c.f. Gothic razn, Old English ærn "house;" see barn) + saka "to search," related to Old Norse soekja "seek" (see seek). Sense influenced by sack (v.). Related: Ransacked; ransacking.