Source : Webster's Revised Unabridged Dictionary (1913)

Behest \Be*hest"\, n. [OE. biheste promise, command, AS.
   beh[=ae]s promise; pref. be- + h[=ae]s command. See {Hest},
   {Hight}.]
   1. That which is willed or ordered; a command; a mandate; an
      injunction.

            To do his master's high behest.       --Sir W.
                                                  Scott.

   2. A vow; a promise. [Obs.]

            The time is come that I should send it her, if I
            keep the behest that I have made.     --Paston.

Behest \Be*hest"\, v. t.
   To vow. [Obs.] --Paston.

Source : WordNet®

behest
     n : an authoritative command or request