noun
1. : a notched or toothed wheel either held in position or turned by an engaging detent, pawl, or click
2. : the retaining wheel over the mainspring arbor of a timepiece
[s]ratchetw.jpg[/s] [
ratchet wheel: 1 wheel, 2 reciprocating lever, 3 pawl for communicating motion, 4 pawl for preventing backward motion
]