runway has 3 distinct synonyms spread across 1 of its 4 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 bar or pair of parallel bars of rolled steel making the railway along which railroad cars or other vehicles can roll
a chute down which logs can slide
Synonyms, antonyms and the broader and narrower relations for runway come from Princeton University’s WordNet. Full sources and licences.
a narrow platform extending from the stage into the audience in a theater or nightclub etc.
a strip of level paved surface where planes can take off and land