Webster's Revised Unabridged Dictionary · 1913

Retinal

Retinal , adjective

(Anatomy) Of or pertaining to the retina.
Collocations (1)
Retinal purple (Physiology Chemistry) , the visual purple.

Retinal , noun

(Chemistry) A retinoid compound (C20H28O), closely related to vitamin A, which is a component of the visual pigments in the eye. It is also called retinaldehyde and vitamin A aldehyde.