offshore rig has 1 distinct synonym spread across 1 of its 1 sense. 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.
drilling rig consisting of an offshore platform (floating or fixed to the sea bed) from which many oil wells can be bored radially
Synonyms, antonyms and the broader and narrower relations for offshore rig come from Princeton University’s WordNet. Full sources and licences.