Definition of third eyelid in English:

third eyelid

Syllabification: third eye·lid

noun

  • informal term for nictitating membrane.
    More example sentences
    • Crocodilians' eyes are immobile spheres covered by three eyelids: the third eyelid, the nictitating membrane, is transparent, but protects the eye from water.
    • Eversion of the nictitating membrane is a condition in which the third eyelid protrudes.
    • These membranes, essentially a third eyelid, can cover the exposed portion of the eye, since, as in all sharks, the upper and lower eyelids of catsharks cannot completely cover the eyeball.

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