Source : Webster's Revised Unabridged Dictionary (1913)

Peninsulate \Pen*in"su*late\, v. t. [imp. & p. p.
   {Peninsulated}; p. pr. & vb. n. {Peninsulating}.]
   To form into a peninsula.

         South River . . . peninsulates Castle Hill farm. --W.
                                                  Bentley.