protest has 4 distinct synonyms spread across 3 of its 6 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.
a formal and solemn declaration of objection
“they finished the game under protest to the league president”
Synonyms, antonyms and the broader and narrower relations for protest come from Princeton University’s WordNet. Full sources and licences.
the act of making a strong public expression of disagreement and disapproval
“he shouted his protests at the umpire”
affirm or avow formally or solemnly
“The suspect protested his innocence”