The Collaborative International Dictionary of English v.0.48:

Monochromatic \Mon`o*chro*mat"ic\, a. [Cf. F. monochromatique.
   See Monochrome.]
   Consisting of one color, or presenting rays of light of one
   color only.
   [1913 Webster]

   Monochromatic lamp (Opt.),a lamp whose flame yields rays of
      some one homogenous light. It is of great importance in
      optical experiments.
      [1913 Webster]