no man's land has 1 distinct synonym spread across 1 of its 3 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.
an unoccupied area between the front lines of opposing armies
land that is unowned and uninhabited (and usually undesirable)
the ambiguous region between two categories or states or conditions (usually containing some features of both)
“but there is still a twilight zone, the tantalizing occurrences that are probably noise but might possibly be a signal”
Synonyms, antonyms and the broader and narrower relations for no man's land come from Princeton University’s WordNet. Full sources and licences.