reserved has no recorded synonym. 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 one recorded opposite is unreserved.
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.
set aside for the use of a particular person or party
marked by self-restraint and reticence
“was habitually reserved in speech, withholding her opinion”
Synonyms, antonyms and the broader and narrower relations for reserved come from Princeton University’s WordNet. Full sources and licences.