An official order or decree issued in opposition to or contradiction of another decree.
From counter- (against) + decree (an official order). Decree comes from Latin decretum. In historical and legal contexts, counterdecrees were official responses to unpopular or opposing decrees, essentially one authority saying 'no' to another authority's command.
Medieval and Renaissance monarchs would issue counterdecrees against each other—imagine being a peasant when two kings issue opposing decrees and you have to figure out which one actually applies to you, which is why this word exists at all.
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