Source : Webster's Revised Unabridged Dictionary (1913)

Refractometer \Re`frac*tom"e*ter\ (r?`fr?k*t?m"?*t?r), n.
   [Refraction + -meter.] (Opt.)
   A contrivance for exhibiting and measuring the refraction of
   light.

Source : WordNet®

refractometer
     n : measuring instrument for measuring the refractive index of a
         substance