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nictitating membrane

noun
1.
a thin membrane, or inner or third eyelid, present in many animals, capable of being drawn across the eyeball, as for protection.
Origin
1705-1715
1705-15; nictate + -ing2
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for nictitating-membrane

nictitating membrane

/ˈnɪktɪˌteɪtɪŋ/
noun
1.
(in reptiles, birds, and some mammals) a thin fold of skin beneath the eyelid that can be drawn across the eye Also called third eyelid, haw
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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nictitating-membrane in Science
nictitating membrane
  (nĭk'tĭ-tā'tĭng)   
A transparent inner eyelid in birds, reptiles, amphibians, and some mammals that protects and moistens the eye without blocking vision.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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