The Collaborative International Dictionary of English v.0.48:

Mediatize \Me"di*a*tize\, v. t. [imp. & p. p. Mediatized; p.
   pr. & vb. n. Mediatizing.] [Cf. F. m['e]diatiser.]
   To cause to act through an agent or to hold a subordinate
   position; to annex; -- specifically applied to the annexation
   during the former German empire of a smaller German state to
   a larger, while allowing it a nominal sovereignty, and its
   prince his rank.
   [1913 Webster]

         The misfortune of being a mediatized prince.
                                                  --Beaconsfield.
   [1913 Webster]