poison has 3 distinct synonyms spread across 2 of its 7 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.
Synonyms, antonyms and the broader and narrower relations for poison come from Princeton University’s WordNet. Full sources and licences.
kill by its poison
“This mushrooms can poison”
administer poison to
“She poisoned her husband but he did not die”
any substance that causes injury or illness or death of a living organism
anything that harms or destroys
“the poison of fascism”