Pronunciation: ( jak'stā"),[key] —n.Naut. 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. See jack rod.