equilibrium has 8 distinct synonyms spread across 3 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 one recorded opposite is disequilibrium.
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 stable situation in which forces cancel one another
a chemical reaction and its reverse proceed at equal rates
equality of distribution
a sensory system located in structures of the inner ear that registers the orientation of the head
Synonyms, antonyms and the broader and narrower relations for equilibrium come from Princeton University’s WordNet. Full sources and licences.