What is the origin of the word knot as a nautical term?

The term "knot" originated sometime around the 16th century and referred to a method of measuring the speed of a sailing vessel. A "chip log" was attached to a line with knots tied at intervals and then thrown overboard. The drag on the chip log caused the line to run out and the number of knots that passed through the mariner's hands over a specific period of time were counted and resulted in a calculation of the speed of the vessel.