Lewis Short
(adjective) : impĕrātīvus (inp-), a, um, impero
* Of or proceeding from a command, commanded: feriae,extraordinary, commanded by a magistrate,Macr. S. 1, 16, § 5 sq.: modus,the imperative,Mart. Cap. 3, § 313, and in the grammarians saep.— Adv.: impĕrātīvē, imperatively, Ulp. Reg. tit. 24, 1.
Charlton T. Lewis, Charles Short, A Latin Dictionary