The Collaborative International Dictionary of English v.0.48:
Tack \Tack\, n. [OE. tak, takke, a fastening; akin to D. tak a
branch, twig, G. zacke a twig, prong, spike, Dan. takke a
tack, spike; cf. also Sw. tagg prickle, point, Icel. t[=a]g a
willow twig, Ir. taca a peg, nail, fastening, Gael. tacaid,
Armor. & Corn. tach; perhaps akin to E. take. Cf. Attach,
Attack, Detach, Tag an end, Zigzag.]
1. A small, short, sharp-pointed nail, usually having a
broad, flat head.
2. That which is attached; a supplement; an appendix. See
Tack, v. t., 3. --Macaulay.
Some tacks had been made to money bills in King
Charles's time. --Bp. Burnet.
(a) A rope used to hold in place the foremost lower
corners of the courses when the vessel is closehauled
(see Illust. of Ship); also, a rope employed to pull
the lower corner of a studding sail to the boom.
(b) The part of a sail to which the tack is usually
fastened; the foremost lower corner of fore-and-aft
sails, as of schooners (see Illust. of Sail).
(c) The direction of a vessel in regard to the trim of her
sails; as, the starboard tack, or port tack; -- the
former when she is closehauled with the wind on her
starboard side; hence, the run of a vessel on one
tack; also, a change of direction; as, to take a
different tack; -- often used metaphorically.
4. (Scots Law) A contract by which the use of a thing is set,
or let, for hire; a lease. --Burrill.
5. Confidence; reliance. [Prov. Eng.] --Halliwell.
Tack of a flag (Naut.), a line spliced into the eye at the
foot of the hoist for securing the flag to the halyards.
Tack pins (Naut.), belaying pins; -- also called jack
To haul the tacks aboard (Naut.), to set the courses.
To hold tack, to last or hold out. --Milton.