red-eye • n. 1. the undesirable effect in flash photography of people appearing to have red eyes, caused by a reflection from the retina when the flashgun is too near the camera lens.2. (also red-eye flight) [in sing.] inf. an overnight or late-night flight on a commercial airline: she caught the red-eye back to New York.3. a freshwater fish with red eyes, in particular a rock bass.4. inf. cheap whiskey.