presumption has 5 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.
(law) an inference of the truth of a fact from other facts proved or admitted or judicially noticed
Synonyms, antonyms and the broader and narrower relations for presumption come from Princeton University’s WordNet. Full sources and licences.
audacious (even arrogant) behavior that you have no right to
“he despised them for their presumptuousness”
a kind of discourtesy in the form of an act of presuming
“his presumption was intolerable”