whitethroat has 6 distinct synonyms spread across 3 of its 3 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.
Old World warbler similar to the greater whitethroat but smaller
greyish-brown Old World warbler with a white throat and underparts
common North American finch with a white patch on the throat and black-and-white striped crown
Synonyms, antonyms and the broader and narrower relations for whitethroat come from Princeton University’s WordNet. Full sources and licences.