Longman Dictionary of Contemporary English - tack

~1 n 1 »NAIL« a small nail with a sharp point and flat top 2 »PIN« AmE a short pin with a large round flat top, for fixing notices to boards, walls etc; drawing pin BrE, thumbtack AmE 3 change tack/try a different tack etc to do something completely different from what you were doing before, especially in order to achieve something  (Rudy changed tack, his tone suddenly becoming friendly.) 4 »SHIP« the direction of a sailing ship, based on the direction of the wind and the position of its sails  (Ships on the starboard tack have right of way.) 5 »SEWING« a long loose stitch used for fastening pieces of cloth together before sewing them properly 6 »UGLY OBJECTS« small objects that are very ugly and cheap, but are sold as decorations  (souvenir shops full of tack) 7 »HORSES« all the equipment you need for horse riding ~2 v 1 T always + adv/prep to fasten something with a tack + up  (tacking notices up on the board) 2 to fasten pieces of cloth together with long loose stitches, before sewing them properly 3 to change the course of a sailing ship so that the wind blows against its sails from the opposite direction tack sth on phr v informal to add something to something that already exists or is complete, especially in a way that looks badly planned  (The environmental section of the bill was obviously tacked on afterwards. | a little porch tacked on to the front of the house)