The Collaborative International Dictionary of English v.0.48:

Magistery \Mag"is*ter*y\, n. [L. magisterium the office of a
   chief, president, director, tutor. See Magistrate.]
   1. Mastery; powerful medical influence; renowned efficacy; a
      sovereign remedy. [Obs.] --Holland.
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   2. A magisterial injunction. [R.] --Brougham.
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   3. (Chem.) A precipitate; a fine substance deposited by
      precipitation; -- applied in old chemistry to certain
      white precipitates from metallic solutions; as, magistery
      of bismuth. --Ure.
      [1913 Webster]