Ratchet \Ratch"et\, 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.

2. A mechanism composed of a ratchet wheel, or ratch, and pawl. See Ratchet wheel, below, and 2d Ratch.

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.

Source: Webster's Revised Unabridged Dictionary (1913)