operative mistake ˌoperative misˈtake noun [countable]
LAW a mistake in a contract that is so serious that it means that the contract has no legal effect
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operative mistake UK US noun [C] LAW
► a mistake in a contract that is serious enough to prevent the contract from being considered legal: »
The judge decided that the description of the goods was so inaccurate that it amounted to an operative mistake.
Financial and business terms. 2012.