Wiktionary
n. The transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility.
Usage examples of "nictating membrane".
Faced with such unknowns, Broey tended to withdraw into himself, eyes veiled by the nictating membrane while he weighed the possibilities.
Manlike in its overall appearance, its face was sharply convex and it had fluttering slits on its nictating membrane swept across the creature's eyes from the inner side to the outer.
A nictating membrane closed over them, as if it were winking at her!
And Balin's nictating membrane was going with the speed of the Morse code.
The nictating membrane that distinguished the exile community from the continental norm flicked over the child's amber eyes and she stared.