What is the X in X-mas?
1550s, "one who chops," agent noun from chop (v.1). Meaning "meat cleaver" is by 1818. Meaning "helicopter" is from 1951, Korean War military slang (cf. egg-beater); as a type of stripped-down motorcycle (originally prefered by Hell's Angels) from 1965.
Teeth, esp false teeth (1930s+)