fair has 17 distinct synonyms spread across 11 of its 17 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. Its 2 recorded opposites are unfair, foul.
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.
(of a baseball) hit between the foul lines
“he hit a fair ball over the third base bag”
gathering of producers to promote business
“world fair”
without favoring one party, in a fair evenhanded manner
“deal fairly with one another”
join so that the external surfaces blend smoothly
2 of the 17 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 fair.
Synonyms, antonyms and the broader and narrower relations for fair come from Princeton University’s WordNet. Full sources and licences.
a competitive exhibition of farm products
“she won a blue ribbon for her baking at the county fair”
a sale of miscellany; often for charity
“the church bazaar”