Tack

(plural tacks)

2012, July 15. Richard Williams in Guardian Unlimited, Tour de France 2012: Carpet tacks cannot force Bradley Wiggins off trackA tough test for even the strongest climber, it was new to the Tour de France this year, but its debut will be remembered for the wrong reasons after one of those spectators scattered carpet tacks on the road and induced around 30 punctures among the group of riders including Bradley Wiggins, the Tour's overall leader, and his chief rivals.

A thumbtack.
(sewing) A loose seam used to temporarily fasten pieces of cloth.
(nautical) The lower corner on the leading edge of a sail relative to the direction of the wind.
(nautical) A course or heading that enables a sailing vessel to head upwind. See also reach, gybe.
A direction or course of action, especially a new one.

1994, Nelson Mandela, Long Walk to Freedom, Abacus 2010, p. 637:I thought that my refusing Barnard would alienate Botha, and decided that such a tack was too risky.

(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.
(nautical) The distance a sailing vessel runs between these maneuvers when working to windward; a board.
(nautical) A rope used to hold in place the foremost lower corners of the courses when the vessel is close-hauled; also, a rope employed to pull the lower corner of a studding sail to the boom.
Any of the various equipment and accessories worn by horses in the course of their use as domesticated animals. Saddles, stirrups, bridles, halters, reins, bits, harnesses, martingales, and breastplates are all forms of horse tack.
(chemistry) The stickiness of a compound, related to its cohesive and adhesive properties.
hardtack

D. H. Lawrence, "Sons and Lovers", 1913:"But if a woman's got nothing but her fair fame to feed on, why, it's thin tack, and a donkey would die of it!"

Bishop BurnetSome tacks had been made to money bills in King Charles's time.

(legal, Scotland) A contract by which the use of a thing is set, or let, for hire; a lease.
(obsolete) Confidence; reliance.

Full definition of tack

To nail with a tack (small nail with a flat head).
To sew/stich with a tack (loose seam used to temporarily fasten pieces of cloth).
(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.
To add something as an extra item.to tack (something) onto (something)
Often paired with "up", to place the tack on a horse.

From an old or dialectal form of French tache. See techy.

(plural tacks)