: a gear through which motion is transmitted by a chain that runs in a groove or engages the cogs of a sprocket wheel
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a gear assembly in which motion is transmitted by means of a chain.
[1875-80]
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chain gear,
a gear for transmitting motion by means of an endless chain, especially one in which the chain transmits motion from one sprocket wheel to another.
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n. a gear transmitting motion by means of a moving endless chain, esp. on a bicycle
Useful english dictionary. 2012.