Sentence:  A <WSD>pawl</WSD> is a sort of catch that fits into a ratchet wheel and pushes it around, or it may be used as a catch to prevent the backward motion of a windlass or the wheel on a derrick. 
Meaning of the word marked with <WSD> tags:  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.