special has 6 distinct synonyms spread across 5 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.
unique or specific to a person or thing or category
“the particular demands of the job”
surpassing what is common or usual or expected
“he paid especial attention to her”
a special offering (usually temporary and at a reduced price) that is featured in advertising
“they are having a special on pork chops”
a dish or meal given prominence in e.g. a restaurant
a television production that features a particular person or work or topic
“the last of a series of BBC specials on Iran is being shown tonight”
2 of the 10 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for special.
Synonyms, antonyms and the broader and narrower relations for special come from Princeton University’s WordNet. Full sources and licences.