Knot
A Dictionary of Law · Henry Campbell Black · 1891
A Dictionary of Law
In seamen's language, a "knot" is a division of the log-line serving to measure the rate of the vessel's motion. The number of knots which run off from the reel in half a minute shows the number of miles the vessel sails in an hour. Hence when a ship goes eight miles an hour she is said to go "eight knots."
Webster.