coast has 5 distinct synonyms spread across 2 of its 5 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.
Synonyms, antonyms and the broader and narrower relations for coast come from Princeton University’s WordNet. Full sources and licences.
a slope down which sleds may coast
“when it snowed they made a coast on the golf course”
the area within view
“the coast is clear”
the act of moving smoothly along a surface while remaining in contact with it
“his slide didn't stop until the bottom of the hill”