What would you call a nautical unit of speed?

A nautical unit of speed is called a knot.

One knot equals exactly one nautical mile per hour, or 1.852 kilometers per hour. The nautical mile is based on Earth’s geometry: it corresponds to one minute of latitude, making knots especially convenient for navigation.

The name comes from the traditional chip log, a device sailors used to estimate a vessel’s speed. A weighted board was thrown overboard while a line with evenly spaced knots ran out. The number of knots passing through a sailor’s hands during a timed interval indicated the ship’s speed.

Knots are still used for ships, aircraft, wind speeds, ocean currents, and tides. A common mix-up is treating “knot” as a distance; it measures speed. The standard abbreviation is “kn,” although “kt” is also widely used, particularly in aviation.