nautical mile

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle, especially an international and US unit equal to 1,852 meters (about 6,076 feet).

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun nautical A unit of length corresponding approximately to one minute of arc of latitude along any meridian. By international agreement it is exactly 1,852 metres (approximately 6,076 feet).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a former British unit of length equivalent to 6,080 feet (1,853.184 meters); 800 feet longer than a statute mile
• noun a unit of length used in navigation; exactly 1,852 meters; historically based on the distance spanned by one minute of arc in latitude