reef has 2 distinct synonyms spread across 1 of its 6 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 submerged ridge of rock or coral near the surface of the water
a rocky region in the southern Transvaal in northeastern South Africa; contains rich gold deposits and coal and manganese
Synonyms, antonyms and the broader and narrower relations for reef come from Princeton University’s WordNet. Full sources and licences.
one of several strips across a sail that can be taken in or rolled up to lessen the area of the sail that is exposed to the wind