Source : Webster's Revised Unabridged Dictionary (1913)

Planimeter \Pla*nim"e*ter\, n. [Plani- + -meter. Cf.
   {Planometer}.]
   An instrument for measuring the area of any plane figure,
   however irregular, by passing a tracer around the bounding
   line; a platometer.

Source : WordNet®

planimeter
     n : a measuring instrument for measuring the area of an
         irregular plane figure [syn: {integrator}]