resistant has 5 distinct synonyms spread across 4 of its 5 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.
relating to or conferring immunity (to disease or infection)
able to tolerate environmental conditions or physiological stress
“the plant is tolerant of saltwater”
disposed to or engaged in defiance of established authority
1 of the 5 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for resistant.
Synonyms, antonyms and the broader and narrower relations for resistant come from Princeton University’s WordNet. Full sources and licences.