ground swell has 1 distinct synonym spread across 1 of its 2 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 obvious change of public opinion or political sentiment that occurs without leadership or overt expression
“there was a ground swell of antiwar sentiment”
Synonyms, antonyms and the broader and narrower relations for ground swell come from Princeton University’s WordNet. Full sources and licences.