third eyelid: meaning, definition, pronunciation and examples
Rare (Specialized/Technical)Technical/Scientific, Zoological, Veterinary
Quick answer
What does “third eyelid” mean?
A thin, protective membrane (nictitating membrane) found in many animals, capable of moving horizontally across the eye for protection and moisture without complete closure.
Audio
Pronunciation
Definition
Meaning and Definition
A thin, protective membrane (nictitating membrane) found in many animals, capable of moving horizontally across the eye for protection and moisture without complete closure.
Used metaphorically to describe a protective or hidden layer/mechanism; in anatomy, refers specifically to the plica semilunaris in humans, a vestigial remnant.
Dialectal Variation
British vs American Usage
Differences
No significant difference in technical meaning. British texts may occasionally use 'haw' colloquially for animals, especially cats and dogs.
Connotations
Neutral and descriptive in both varieties. The term carries no cultural connotation.
Frequency
Equally rare in both dialects, confined to specialist fields.
Grammar
How to Use “third eyelid” in a Sentence
The [animal] has/possesses a third eyelid.The third eyelid [verbs: moves, sweeps, protects].Vocabulary
Collocations
Examples
Examples of “third eyelid” in a Sentence
noun
British English
- The veterinarian examined the dog's inflamed third eyelid.
- In birds, the third eyelid acts like a windscreen wiper.
American English
- The hawk's third eyelid swept across its eye as it dove.
- Cherry eye is a prolapse of the gland in the third eyelid.
Usage
Meaning in Context
Business
Not used.
Academic
Used in biology, zoology, veterinary medicine, and comparative anatomy papers.
Everyday
Virtually never used unless discussing specific animal health or anatomy.
Technical
Precise term for the nictitating membrane in vertebrates.
Vocabulary
Synonyms of “third eyelid”
Vocabulary
Antonyms of “third eyelid”
Watch out
Common Mistakes When Using “third eyelid”
- Using 'third eyelid' to refer to a human's upper or lower eyelid.
- Assuming it is a common, functional part of human anatomy.
FAQ
Frequently Asked Questions
Humans have a vestigial remnant called the plica semilunaris, a small fold of tissue in the inner corner of the eye. It is not a functional third eyelid.
Birds, reptiles, amphibians, fish, and some mammals (like cats, dogs, camels, and polar bears) have a functional nictitating membrane.
Yes, 'haw' is a common colloquial term for the visible third eyelid in animals, especially when it is protruding due to illness or relaxation.
Often not when the animal is alert. It may become briefly visible during blinking or sleep. Persistent visibility can indicate illness, dehydration, or injury.
A thin, protective membrane (nictitating membrane) found in many animals, capable of moving horizontally across the eye for protection and moisture without complete closure.
Third eyelid is usually technical/scientific, zoological, veterinary in register.
Third eyelid: in British English it is pronounced /ˌθɜːd ˈaɪ.lɪd/, and in American English it is pronounced /ˌθɝːd ˈaɪ.lɪd/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “[No common idioms]”
Learning
Memory Aids
Mnemonic
Think: TWO is normal for you, but birds and reptiles need a THIRD to protect and clear.
Conceptual Metaphor
A HIDDEN SHIELD; A SECRET DEFENSE MECHANISM.
Practice
Quiz
What is the primary function of a third eyelid in many animals?