The semicircular, forward-facing end of a spar, designed to cup the mast and allow the spar to pivot horizontally and vertically. Jaws are typically secured around the back of the mast by a parrel bead line or wire, keeping the spar attached while hoisting, lowering, or swinging the sail.
Heard on the job
Grease the mast where the gaff jaw rides so it doesn't bind when we hoist.