noun

1. a short nail or pin, with a narrow shaft that is not tapered and a relatively large, flat head
2. 1. the act of fastening, esp. in a slight or temporary way
   2. Sewing a stitch for marking darts, etc. from a pattern, clipped and later removed
      in full tailor's tack
   3. stickiness; adhesiveness
3. a zigzag course, or movement in such a course
4. a course of action or policy, esp. one differing from another or a preceding course

5. Etymology: < ?

   food; foodstuff hardtack
6. Naut.
   1. a rope for securing the forward lower corner of a fore-and-aft sail
   2. this corner
   3. the direction in which a vessel is moving in relation to the position of the sails
   4. a change of direction in which the sail or sails shift from one side of the vessel to the other
   5. a course against the wind
   6. any of a series of zigzag movements in such a course
7. equipment for riding a horse, as saddles, bridles, etc.; saddlery

Etymology: ME takke < MDu tacke, twig, point, akin to Ger zacke < ? IE base *dek-, to tear > tail

transitive verb

1. to fasten or attach with tacks
2. to attach temporarily, as by sewing with long stitches
3. to attach as a supplement; add to tack an amendment onto a bill
4. Horsemanship to put a saddle, bridle, etc. on (a horse): often with up
5. Naut.
   1. to change the course of (a vessel) by turning its bow into and across the wind
   2. to maneuver (a vessel) against the wind by a series of tacks

intransitive verb

1. Naut.
   1. to tack a sailing vessel
   2. to change its course by being tacked, or sail against the wind by a series of tacks: said of a sailing vessel
2. to go in a zigzag course
3. to change suddenly one's policy or course of action