Source : Webster's Revised Unabridged Dictionary (1913)

Melanin \Mel"a*nin\, n. [Gr. me`las, -anos, black.] (Physiol.)
   A black pigment found in the pigment-bearing cells of the
   skin (particularly in the skin of the negro), in the
   epithelial cells of the external layer of the retina (then
   called {fuscin}), in the outer layer of the choroid, and
   elsewhere. It is supposed to be derived from the
   decomposition of hemoglobin.

Source : WordNet®

melanin
     n : insoluble pigments that account for the color of e.g. skin
         and scales and feathers