The Collaborative International Dictionary of English v.0.48:

Spectrophotometer \Spec`tro*pho*tom"e*ter\, n. [Spectrum +
   photometer.]
   1. (Opt.) An instrument for measuring or comparing the
      intensities of the colors of the spectrum.
      [1913 Webster]

   2. (Chem., Physics) An analytical instrument for measuring
      the degree of absorption of light at different wavelengths
      by a chemical substance. A specific pattern of absorption
      intensities at a series of wavelengths is a characteristic
      of each different chemical substance.
      [PJC]

WordNet (r) 3.0 (2006):

spectrophotometer
    n 1: a photometer for comparing two light radiations wavelength
         by wavelength