pawl

Short definition from Wiktionary

Noun

1. 1
   A pivoted catch designed to fall into a notch on a ratchet wheel so as to allow movement in only one direction (e.g. on a windlass or in a clock mechanism), or alternatively to move the wheel in one direction.
2. 2
   A similar device to prevent motion in other mechanisms besides ratchets.
3. 3
   Alternative form of paul (“kind of tent”).

Verb

1. 1
   To stop with a pawl.