What is the X in X-mas?
late 12c., probably from Old English *stagga "stag," from Proto-Germanic *stag- (see sting). The Old Norse equivalent was used of male foxes, tomcats and dragons and the Germanic root word perhaps originally meant "male animal in its prime." Meaning "pertaining to or composed of males only" (stag party) is American English slang from 1848. Stag film "pornographic movie" is attested from 1968.