The Collaborative International Dictionary of English v.0.48:

Prescribe \Pre*scribe"\, v. t. [imp. & p. p. Prescribed; p. pr
   & vb. n. Prescribing.] [L. praescribere, praescriptum; prae
   before + scriebe to write. See Scribe.]
   [1913 Webster]
   1. To lay down authoritatively as a guide, direction, or rule
      of action; to impose as a peremptory order; to dictate; to
      appoint; to direct.
      [1913 Webster]

            Prescribe not us our duties.          --Shak.
      [1913 Webster]

            Let streams prescribe their fountains where to run.
                                                  --Dryden.
      [1913 Webster]

   2. (Med.) To direct, as a remedy to be used by a patient; as,
      the doctor prescribed quinine.
      [1913 Webster]

   Syn: To appoint; order; command; dictate; ordain; institute;
        establish.
        [1913 Webster]

WordNet (r) 3.0 (2006):

prescribed
    adj 1: set down as a rule or guide
    2: fixed or established especially by order or command; "at the
       time appointed (or the appointed time") [syn: appointed,
       decreed, ordained, prescribed]
    3: conforming to set usage, procedure, or discipline; "in
       prescribed order" [syn: official, prescribed]
    4: formally laid down or imposed; "positive laws" [syn:
       positive, prescribed]