<p><strong>Noun</strong></p><ul><li>a short, sharp-pointed nail, usually with a flat, broad head.</li><li>Nautical: a rope for extending the lower forward corner of a course.</li><li>the lower forward corner of a course or fore-and-aft sail.</li><li>the heading of a sailing vessel, when sailing close-hauled, with reference to the wind direction.</li><li>a course run obliquely against the wind.</li><li>one of the series of straight runs that make up the zigzag course of a ship proceeding to windward.</li><li>a course of action or conduct, especially one differing from some preceding or other course.</li><li>one of the movements of a zigzag course on land.</li><li>a stitch, especially a long stitch used in fastening seams, preparatory to a more thorough sewing.</li><li>a fastening, especially of a temporary kind.</li><li>stickiness, as of nearly dry paint or glue or of a printing ink or gummed tape; adhesiveness.</li><li>the gear used in equipping a horse, including saddle, bridle, martingale, etc.</li></ul><p><strong>Verb</strong></p><ul><li>to fasten by a tack or tacks: to tack a rug to the floor.</li><li>to secure by some slight or temporary fastening.</li><li>to join together; unite; combine.</li><li>to attach as something supplementary; append; annex (often followed by on or onto).</li><li>Nautical: to change the course of (a sailing vessel) to the opposite tack.</li><li>to navigate (a sailing vessel) by a series of tacks.</li><li>to equip (a horse) with tack.</li></ul><p><strong>Verb (used without object)</strong></p><ul><li>Nautical: to change the course of a sailing vessel by bringing the head into the wind and then causing it to fall off on the other side.</li><li>(of a sailing vessel): to change course in this way.</li><li>to proceed to windward by a series of courses as close to the wind as the vessel will sail.</li><li>to take or follow a zigzag course or route.</li><li>to change one's course of action, conduct, ideas, etc.</li><li>to equip a horse with tack (usually followed by up): Please tack up quickly.</li></ul><p><strong>End of Response</strong></p>