third eyelid third eye • third gear · · · Info · Definitions · Synonyms · Characters · · third eyelid · · Text Common · · Latin · · Scripts 12 · · Length 5 · · Syllables Definitions · · · (noun) a protective fold of skin in the eyes of reptiles and birds and some mammals. Synonyms: nictitating membrane, third eyelid. · · Noun Definition 1 Synonyms · · · nictitating membrane · · Synonym 1 Characters · · space U+0020 d latin small letter d U+0064 e latin small letter e U+0065 h latin small letter h U+0068 i latin small letter i U+0069 l latin small letter l U+006C r latin small letter r U+0072 t latin small letter t U+0074 y latin small letter y U+0079