jackstay

noun Nautical.

1. a rod or batten, following a yard, gaff, or boom, to which one edge of a sail is bent.
2. a rail for guiding the movement of the hanks of a sail.
3. a transverse stay for stiffening a mast having a gaff sail, coming downward and outward from the head of the mast, passing over a spreader at the level of the gaff, then inclining inward to the mast again near the foot.
4. jack rod.

noun nautical

1. a metal rod, wire rope, or wooden batten to which an edge of a sail is fastened along a yard
2. a support for the parrel of a yard