Real Dictionary

red eye in British English
designating a late-night or all-night commercial airline flight
such a flight
adjective: of or indicating a long-distance flight that leaves late at night
noun: an aeroplane flight leaving late at night or arriving early in the morning
noun: an undesirable effect that sometimes appears in flashlight portraits when light from the flash enters the eye and is reflected from the retina onto the film, producing a red colour
noun: the condition of having bloodshot eyes, as from eyestrain or lack of sleep

red-eye
countable noun: A red-eye or a red-eye flight is a plane journey during the night.