[ sleep-lis ]
/ ˈslip lɪs /


without sleep: a sleepless night.
watchful; alert: sleepless devotion to duty.
always active: the sleepless ocean.

Nearby words

  1. sleeping partner,
  2. sleeping pill,
  3. sleeping policeman,
  4. sleeping porch,
  5. sleeping sickness,
  6. sleeplessly,
  7. sleepover,
  8. sleepshirt,
  9. sleepwalk,
  10. sleepwalking

Origin of sleepless

late Middle English word dating back to 1375–1425; see origin at sleep, -less

Related formssleep·less·ly, adverbsleep·less·ness, noun Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for sleepless

British Dictionary definitions for sleepless


/ (ˈsliːplɪs) /


without sleep or resta sleepless journey
unable to sleep
always watchful or alert
mainly poetic always active or movingthe sleepless tides
Derived Formssleeplessly, adverbsleeplessness, noun

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for sleepless



early 15c., from sleep (n.) + -less. Old English had slæpleas but the modern word seems to be a re-formation. Cf. German schlaflos, Dutch slapeloos. Related: Sleeplessly; sleeplessness.

Online Etymology Dictionary, © 2010 Douglas Harper