tack¹ / tak/ • n. 1. a small, sharp, broad-headed nail. ∎  a thumbtack.2. a long stitch used to fasten fabrics together temporarily, prior to permanent sewing.3. Sailing an act of changing course by turning a vessel's head into and through the wind, so as to bring the wind on the opposite side. ∎  a boat's course relative to the direction of the wind: the brig bowled past on the opposite tack. ∎  a distance sailed between such changes of course. ∎ fig. a method of dealing with a situation or problem; a course of action or policy: as she could not stop him from going she tried another tack and insisted on going with him.4. Sailing a rope for securing the weather clew of a course. ∎  the weather clew of a course, or the lower forward corner of a fore-and-aft sail.5. the quality of being sticky: cooking the sugar to caramel gives tack to the texture.• v. 1. [tr.] fasten or fix in place with tacks: he used the tool to tack down sheets of fiberboard. ∎  fasten (pieces of cloth) together temporarily with long stitches. ∎  (tack something on) add or append something to something already existing: long-term savings plans with some life insurance tacked on.2. [intr.] Sailing change course by turning a boat's head into and through the wind.Compare with wear² . ∎  [tr.] alter the course of (a boat) in such a way. ∎  make a series of such changes of course while sailing: she spent the entire night tacking back and forth. ∎ fig. make a change in one's conduct, policy, or direction of attention: he answered, but she had tacked and was on a new tangent.PHRASES: on the port (or starboard) tack Sailing with the wind coming from the port (or starboard) side of the boat.DERIVATIVES: tack·er n.tack² • n. equipment used in horseback riding, including the saddle and bridle.• v. [tr.] (usu. tack up) put tack on (a horse): he was cooperative about being tacked up and groomed.

tack1
A. fastening, as a clasp, sharp-pointed nail, etc. XIV.

B. (naut.) rope, wire, etc. to secure sails XV. Parallel to later tach(e), the two forms presumably repr. OF. vars. *taque, (dial.) tache.
So tack vb. A. †attach XIV; fasten loosely or temporarily XV; B. (naut.; from sense B of the sb.) shift the tacks in going about XVI.

tack2 food-stuff, as in hard t. ship's biscuit, XIX. of unkn. orig.