cam (n.1)

1777, "a projecting part of a rotating machinery used to impart motion to another part," from Dutch cam "cog of a wheel," originally "comb," from Proto-Germanic *kambaz "comb," from PIE root *gembh- "tooth, nail." It is thus a cognate of English comb (n.). This might have combined with English camber "having a slight arch;" or the whole thing could be from camber. It converts regular rotary motion into irregular, fast-and-slow rotary or reciprocal motion. "The original method was by cogs or teeth fixed or cut at certain points in the circumference or disc of a wheel ..." [OED]. Cam-shaft attested from 1850.

cam (n.2)

abbreviation of camera, by 1990.

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Definitions of cam from WordNet
cam (n.)
a rotating disk shaped to convert circular into linear motion;
Cam (n.)
a river in east central England that flows past Cambridge to join the Ouse River;
Synonyms: River Cam / Cam River