The Collaborative International Dictionary of English v.0.48:

Magistrature \Mag"is*tra`ture\, n. [Cf. F. magistrature.]
   Magistracy. [Obs.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

magistrature
    n 1: the position of magistrate [syn: magistracy,
         magistrature]