The quality or condition of occurring or existing at exactly the same moment in time.
From coinstantaneous + -ity (suffix forming abstract nouns). Builds on the prefix co- (together) + instantaneous (from Latin instantia: in- (in) + stans (standing)). Rare philosophical term from 17th-18th century metaphysics.
Medieval philosophers obsessed over this: if two events happen at exactly the same microsecond, can one cause the other? This word was their way of talking about perfect temporal overlap, a problem that still puzzles physicists.
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