A formal decree or edict, especially one issued by a pope or by a church council in medieval times.
Latin decretum, neuter past participle of decernere (to decide, determine). The word was widely used in ecclesiastical contexts, and many famous collections bear the name 'decretum' (like Gratian's Decretum).
Gratian's Decretum, compiled around 1140, was basically the medieval church's legal constitution—it became so influential that popes and bishops cited it for centuries as the foundation of canon law.
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