sea mile

(navigation) An approximate mean value of the nautical mile equal to 6080 feet (1853.184 meters) or the length of a minute of arc along the meridian at latitude 48°.

A unit of distance equal to a minute of arc of a great circle and varying (because the earth is not a perfect sphere) between approximately 2, 014 yards (1, 842 meters) at the equator and 2, 035 yards (1, 861 meters) at the pole. Compare with nautical mile.

See the Introduction, Abbreviations and Pronunciation for further details.

length British One minute of latitude locally, but sometimes a synonym for nautical mile; see geographic mile.

The noun has one meaning:

Meaning #1: a former British unit of length once used in navigation; equivalent to 1828.8 meters (6000 feet)
  Synonym: mile