A medieval scholar or expert in church law, particularly one who studied and interpreted papal decrees and the Decretals.
From 'decretal' plus '-ist' (one who practices or specializes in). Medieval universities had many decretalists who were essentially church lawyers studying canon law.
A medieval 'decretalist' was basically a lawyer with a religious degree—they spent their lives reading the Pope's official edicts and explaining what they meant in court!
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