‖ decretum|dɪˈkriːtəm| [L.] A decree; sometimes short for Decretum Gratiani. 1602W. Watson Decacordon 163 The decretum of the order obserued in all elections.1888Encycl.Brit. XXIV. 639/1 The Decretum specially inculcated subjection of the wife to the husband.