A unit of length used in ancient Greece, equal to 100 Greek feet (varying locally, but equal to approx. 30.8 metres, 101 feet).
Early 17th century; earliest use found in John Bingham (fl. c1616). From ancient Greek πλέθρον measure of length of 100 feet, unit of area of 10,000 square feet, i.e. equal to that of a square with sides of one plethron; of unknown origin.