ruin has 11 distinct synonyms spread across 8 of its 12 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.
an irrecoverable state of devastation and destruction
“you have brought ruin on this entire family”
a ruined building
“they explored several Roman ruins”
an event that results in destruction
destruction achieved by causing something to be wrecked or ruined
reduce to ruins
“The country lay ruined after the war”
Synonyms, antonyms and the broader and narrower relations for ruin come from Princeton University’s WordNet. Full sources and licences.