cam (n.1)youdaoicibaDictYouDict[cam 词源字典]
"a projecting part of a rotating machinery," 1777, from Dutch cam "cog of a wheel," originally "comb;" cognate of English comb (n.). This might have combined with English camber "having a slight arch;" or the whole thing could be from camber.[cam etymology, cam origin, 英语词源]
cam (n.2)youdaoicibaDictYouDict
abbreviation of camera, by 1990.