Knot. (See also Nautical Mile). A knot is 1 nautical mile per hour and is the measurement unit for speed of vessels and also aircraft.
Nautical mile. This is the unit of distance used at sea. It is the length of one minute of latitude and this varies from the equator to the poles. For convenience a standard nautical mile is assumed to be 1,852 metres or 6,080 feet, which is the true length of a nautical mile in about latitude 52 degrees.