thresher has 5 distinct synonyms spread across 2 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.
a farm machine for separating seeds or grain from the husks and straw
large pelagic shark of warm seas with a whiplike tail used to round up small fish on which to feed
Synonyms, antonyms and the broader and narrower relations for thresher come from Princeton University’s WordNet. Full sources and licences.