Having the nature of or relating to a decree; characterized by making official decisions or pronouncements.
From Latin decretivus, formed from decernere (to decide, decree) + -ive (having the quality of). The suffix -ive transforms the Latin verb into an adjective describing something that has the quality of decreeing.
This word is rarely used in modern English, but it perfectly captures the idea of something being authoritatively decided—it's the adjective form of the act of decreeing itself.
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