a stain; a tache.-a peculiar flavor or taint; as, a musty tack.-a small, short, sharp-pointed nail, usually having a broad, flat head.-that which is attached; a supplement; an appendix. see tack, v. t., 3.-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.-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).-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.-a contract by which the use of a thing is set, or let, for hire; a lease.-confidence; reliance.-to fasten or attach.-especially, to attach or secure in a slight or hasty manner, as by stitching or nailing; as, to tack together the sheets of a book; to tack one piece of cloth to another; to tack on a board or shingle; to tack one piece of metal to another by drops of solder.-in parliamentary usage, to add (a supplement) to a bill; to append; -- often with on or to.-to change the direction of (a vessel) when sailing closehauled, by putting the helm alee and shifting the tacks and sails so that she will proceed to windward nearly at right angles to her former course.-to change the direction of a vessel by shifting the position of the helm and sails; also (as said of a vessel), to have her direction changed through the shifting of the helm and sails. see tack, v. t., 4.