nautical mile has 7 distinct synonyms spread across 2 of its 2 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a former British unit of length equivalent to 6,080 feet (1,853.184 meters); 800 feet longer than a statute mile
a unit of length used in navigation; exactly 1,852 meters; historically based on the distance spanned by one minute of arc in latitude
Synonyms, antonyms and the broader and narrower relations for nautical mile come from Princeton University’s WordNet. Full sources and licences.