Toothed wheels that mesh with other wheels to transmit motion in machinery. Can also refer to small, subordinate parts of a larger system.
From Middle English 'cogge', possibly from Old Norse 'kǫggr' meaning a type of ship with projecting timber pieces. The mechanical meaning developed from the resemblance to ship construction elements.
The phrase 'cog in the machine' originally had positive connotations, suggesting essential functionality, but modern usage often implies being replaceable or insignificant. Interestingly, the first cogs were actually wooden teeth inserted into wheel rims.
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