1 pin, push-pin, nail, Brit drawing-pin, tin-tack, US thumbtack:
Someone keeps stealing the tacks from the bulletin board.
2 fastening, stitch, baste:
Could you put some tacks in the hem so I can try on the skirt?
3 direction, bearing, heading, course, approach; way, path, procedure, method, technique, attack, line:
Our new tack was due east. They may have to take a different tack to win the contract.
4 tackle, gear, equipment, equipage, harness, saddlery, fittings, fitments, kit, outfit, rig, rigging, accoutrements or US also accouterments:
He has ordered all new tack for his horse.
5 pin, attach, fasten, secure, join, couple, unite, combine, stick, fix, affix, staple, nail, skewer, peg, screw, bolt, rivet; baste, stitch, sew, bind, tie; paste, glue, cement, solder, braze, weld:
You were only supposed to tack these together lightly, but now I can't pull them apart.
6 change direction or heading or course, Nautical go or come about; zigzag, veer off or away, Nautical beat:
We tacked quickly to avoid striking the buoy.
7 tack on. add (on), append, annex, attach, tag on:
When they tacked on a rider to the contract, we refused to sign it.