nictitating membrane
Definition of nictitating membrane
noun
Zoology- a whitish or translucent membrane that forms an inner eyelid in birds, reptiles, and some mammals. It can be drawn across the eye to protect it from dust and keep it moist. Also called third eyelid.
Origin:
early 18th century: nictitating based on medieval Latin nictitat- 'blinked', frequentative of nictare