What is the X in X-mas?
Old English wæpen "instrument of fighting and defense," from Proto-Germanic *wæpnan (cf. Old Saxon wapan, Old Norse vapn, Danish vaaben, Old Frisian wepin, Middle Dutch wapen, Old High German waffen, German wafen (neuter), waffe (fem.)), from *webno-m, of unknown origin with no cognates outside Germanic.
The buttocks; anus; ass
[1970s+; perhaps a variant of kazoo]