trill has 3 distinct synonyms spread across 2 of its 4 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.
the articulation of a consonant (especially the consonant `r') with a rapid flutter of the tongue against the palate or uvula
“he pronounced his R's with a distinct trill”
pronounce with a trill, of the phoneme `r'
“Some speakers trill their r's”
Synonyms, antonyms and the broader and narrower relations for trill come from Princeton University’s WordNet. Full sources and licences.