Added 10 October 2026 sleeplessness noun Categories: Describing WordsRare Words noun ! Definition from Wiktionary (CC BY-SA). More about sleeplessness at Wordnik → Where our words come from → Lack of sleep; the property of being sleepless; the inability to sleep, insomnia. Related Words: wakefulnessinsomniasleepinessslumberlessnessinsomnolencyunsleepinsomnolencebedlessnesswakelessnesslustlessness Back to today's word