To take in part of a sail in order to adapt the size of the sail to the force of the wind.
To pull or yank strongly, especially in relation to horse riding.
(of paddles) To move the floats of a paddle wheel toward its center so that they will not dip so deeply.
Reef the paddles.
The process of reefing (taking in a sail); an act of reefing; also used of clothing.
A reef (seam of quartz).