n.
Pronunciation: ˌ ī - ə - ' däp-s ə n
Function: noun
Etymology: iod- (fr. Greek ioeid ē s violet colored) + Greek ops is sight, vision + English -in ― more at OPTIC
Date: 1938
: a photosensitive violet pigment in the retinal cones that is similar to rhodopsin but more labile, is formed from vitamin A, and is important in daylight vision