Definition of nictitating membrane in US English:

nictitating membrane


  • 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
    • ‘When some kingfishers dive for fish, their eyes are covered by a nictitating membrane.’
    • ‘They have a full inner eyelid, or nictitating membrane, which protects the eye from damage and drying.’
    • ‘Many species of shark have a nictitating membrane that acts like our eyelid to protect the eye from injury.’
    • ‘Other signs are a visible shiver - their whole body shakes - and flickering of their nictitating membranes.’
    • ‘Crocodilians' eyes are immobile spheres covered by three eyelids: the third eyelid, the nictitating membrane, is transparent, but protects the eye from water.’


Early 18th century: nictitating based on medieval Latin nictitat- ‘blinked’, frequentative of nictare.


nictitating membrane

/ˌniktətādiNG ˈmembrān/