duck has 13 distinct synonyms spread across 3 of its 8 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.
small wild or domesticated web-footed broad-billed swimming bird usually having a depressed body and short legs
a heavy cotton fabric of plain weave; used for clothing and tents
to move (the head or body) quickly downwards or away
“Before he could duck, another stone struck him”
Synonyms, antonyms and the broader and narrower relations for duck come from Princeton University’s WordNet. Full sources and licences.