A fathom is a unit of length in the imperial and the U.S. customary systems equal to 6 feet (1.8288 metres), used especially for measuring the depth of water. There are two yards (6 feet) in an imperial fathom. Originally based on the distance between a mans outstretched arms, the size of a fathom has varied slightly depending on whether it was defined as a thousandth of an (Admiralty) nautical mile or as a multiple of the imperial yard. Formerly, the term was used for any of several units of length varying around 5–5 1/2 feet (1.5–1.7 m). The name derives from the Old English word fæðm, corresponding to the Old High German word "fadum" meaning embracing arms or a pair of outstretched arms. In Middle English it was fathme. A cable length, based on the length of a ships cable, has been variously reckoned as equal to 100 or 120 fathoms. At one time, a quarter meant one-fourth of a fathom.