Source : Webster's Revised Unabridged Dictionary (1913)

Polarimeter \Po`lar*im"e*ter\, n. [Polar + -meter.] (Opt.)
   An instrument for determining the amount of polarization of
   light, or the proportion of polarized light, in a partially
   polarized ray.

Source : WordNet®

polarimeter
     n : an optical device used to measure the rotation of the plane
         of vibration of polarized light [syn: {polariscope}]