dim has 17 distinct synonyms spread across 8 of its 10 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.
become dim or lusterless
“the lights dimmed and the curtain rose”
make dim or lusterless
“Time had dimmed the silver”
become vague or indistinct
“The distinction between the two theories blurred”
made dim or less bright
“the dimmed houselights brought a hush of anticipation”
Synonyms, antonyms and the broader and narrower relations for dim come from Princeton University’s WordNet. Full sources and licences.