/roh dop"sin/ , n. Biochem.
a bright-red photosensitive pigment found in the rod-shaped cells of the retina of certain fishes and most higher vertebrates: it is broken down by the action of dim light into retinal and opsin. Also called visual purple .
[ 1885-90; RHOD- + Gk óps ( is ) sight, vision + -IN 2 ]