■ noun
each of several projections on the rim of a wheel that engage with the links of a chain or with holes in film, tape, or paper.
(also sprocket wheel) a wheel with projections of this kind.

C16 (denoting a triangular piece of timber used in a roof): of unknown origin.
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EngMac
sprocket
n. 1. (исто и sprocket-wheel) запченик.; 2. забец (на запченик)
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Merriam-Webster Collegiate® Dictionary
sprock·et
Pronunciation: ‘sprä-kət
Function: noun
Etymology: origin unknown
Date: 1886

1 : a toothed wheel whose teeth engage the links of a chain
2 : a cylinder with teeth around the circumference at either end that project through perforations in something (as motion-picture film) to move it through a mechanism (as a projector)