n (nautical) The maneuver by which a sailing vessel turns its bow through the wind so that the wind changes from one side to the other.
n (nautical) The distance a sailing vessel runs between these maneuvers when working to windward; a board.
n Any of the various equipment and accessories worn by horses in the course of their use as domesticated animals. saddle|Saddles, stirrups, bridles, halters, reins, bits, harnesses, martingales, and breastplates are all forms of horse 'tack'.
v (nautical) To maneuver a sailing vessel so that its bow turns through the wind, i.e. the wind changes from one side of the vessel to the other.