'Nictitating membrane' definitions:

Definition of 'nictitating membrane'

From: WordNet
noun
A protective fold of skin in the eyes of reptiles and birds and some mammals [syn: nictitating membrane, third eyelid]

Definition of 'Nictitating membrane'

From: GCIDE
  • Nictitate \Nic"ti*tate\, v. i. [See Nictate.] To wink; to nictate. [1913 Webster]
  • Nictitating membrane (Anat.), a thin membrane, found in many animals at the inner angle, or beneath the lower lid, of the eye, and capable of being drawn across the eyeball; the third eyelid; the haw. [1913 Webster]