benevolent has 10 distinct synonyms spread across 3 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.
showing or motivated by sympathy and understanding and generosity
“was charitable in his opinions of others”
generous in providing aid to others
generous in assistance to the poor
“a benevolent contributor”
1 of the 4 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 benevolent.
Synonyms, antonyms and the broader and narrower relations for benevolent come from Princeton University’s WordNet. Full sources and licences.