The Collaborative International Dictionary of English v.0.48:

Behest \Be*hest"\, v. t.
   To vow. [Obs.] --Paston.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            To do his master's high behest.       --Sir W.
                                                  Scott.
      [1913 Webster]

   2. A vow; a promise. [Obs.]
      [1913 Webster]

            The time is come that I should send it her, if I
            keep the behest that I have made.     --Paston.
      [1913 Webster]

WordNet (r) 3.0 (2006):

behest
    n 1: an authoritative command or request

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "behest":
   bidding, charge, command, commandment, demand, dictate, dictation,
   direct order, hest, imperative, injunction, mandate, order,
   pleasure, prompting, request, say-so, solicitation, special order,
   will, word, word of command