peace has 9 distinct synonyms spread across 3 of its 5 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 one recorded opposite is war.
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.
harmonious relations; freedom from disputes
“the roommates lived in peace together”
the absence of mental stress or anxiety
the general security of public places
“he was arrested for disturbing the peace”
a treaty to cease hostilities
“peace came on November 11th”
Synonyms, antonyms and the broader and narrower relations for peace come from Princeton University’s WordNet. Full sources and licences.