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The Collaborative International Dictionary of English v.0.48 (gcide)

Ratchet \Ratch"et\ (-[e^]t), n. [Properly a diminutive from the
same word as rack: cf. F. rochet. See 2d {Ratch}, {Rack} the
instrument.]
1. A pawl, click, or detent, for holding or propelling a
ratchet wheel, or ratch, etc.
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2. A mechanism composed of a ratchet wheel, or ratch, and
pawl. See {Ratchet wheel}, below, and 2d {Ratch}.
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{Ratchet brace} (Mech.), a boring brace, having a ratchet
wheel and pawl for rotating the tool by back and forth
movements of the brace handle.

{Ratchet drill}, a portable machine for working a drill by
hand, consisting of a hand lever carrying at one end a
drill holder which is revolved by means of a ratchet wheel
and pawl, by swinging the lever back and forth.

{Ratchet wheel} (Mach.), a circular wheel having teeth,
usually angular, with which a reciprocating pawl engages
to turn the wheel forward, or a stationary pawl to hold it
from turning backward.
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Note: In the cut, the moving pawl c slides over the teeth in
one direction, but in returning, draws the wheel with
it, while the pawl d prevents it from turning in the
contrary direction.
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