The Collaborative International Dictionary of English v.0.48:

Magistral \Mag"is*tral\, a. [L. magistralis: cf. F. magistral.
   See Magistrate.]
   1. Pertaining to a master; magisterial; authoritative;
      dogmatic.
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   2. Commanded or prescribed by a magister, esp. by a doctor;
      hence, effectual; sovereign; as, a magistral sirup. "Some
      magistral opiate." --Bacon.
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   3. (Pharmacy) Formulated extemporaneously, or for a special
      case; -- opposed to officinal, and said of prescriptions
      and medicines. --Dunglison.
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   Magistral line (Fort.), the guiding line, or outline, by
      which the form of the work is determined. It is usually
      the crest line of the parapet in fieldworks, or the top
      line of the escarp in permanent fortifications.
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