pro has 1 distinct synonym spread across 1 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. Its 2 recorded opposites are con, anti.
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.
an athlete who plays for pay
in favor of (an action or proposal etc.)
“a pro vote”
in favor of a proposition, opinion, etc.
Synonyms, antonyms and the broader and narrower relations for pro come from Princeton University’s WordNet. Full sources and licences.