- red-eye (n.)
- "airplane flight which deprives travelers of sleep," 1968, from the red eyes of sleeplessness; earlier as a noun meaning "raw and inferior whiskey" (1819, American English).
- sleepless (adj.)
- early 15c., from sleep (n.) + -less. Old English had slæpleas but the modern word seems to be a re-formation. Similar formation in German schlaflos, Dutch slapeloos. Related: Sleeplessly; sleeplessness.