kt is a short written form of knot, the unit people use for how fast a ship or a plane is moving. One knot is one nautical mile in one hour — a bit more than a usual land mile in an hour, though you do not need the exact number to use the word. You will see kt in flying, in shipping, and in weather reports for wind at sea (for example wind 20 kt). Say “knot” out loud, not “kay-tee”. Though actually, jewellery shops also write kt for karat, the measure of how pure gold is. Same letters, completely different job. In this sense, kt is only the speed word.