sleepless

adjective

sleep·​less ˈslēp-ləs 

1

: not able to sleep

lay sleepless with fever

2

: affording no sleep

sleepless nights

3

: unceasingly active or operative

sleepless casinos

sleeplessly adverb

sleeplessness noun

Synonyms of sleepless

• wakeful
• awake

Examples of sleepless in a Sentence

He lay sleepless in bed.

Recent Examples on the Web

There were certainly plenty of long days and sleepless nights along the way, but seeing the finished space and what it has become made all of that hard work worthwhile. — Blaine Callahan, Hartford Courant, 7 Sep. 2026

Nelson remembers hushing her foster children back to sleep that night and calling 911, anxious for an end to those sleepless nights. — Kendrick Calfee, Kansas City Star, 2 Sep. 2026

This month, her mother’s memory-care facility was in an evacuation zone, causing many sleepless nights. — Anya Kamenetz, Curbed, 28 Aug. 2026

The London musician’s forlorn and otherworldly new industrial track passes a sleepless night. — Marshall Gu, Pitchfork, 28 Aug. 2026

Word History

First Known Use

15th century, in the meaning defined at sense 1

Kids Definition

sleepless

adjective

sleep·​less ˈslē-pləs 

1

: not able to sleep

2

: marked by the absence of sleep

a sleepless night

3

: unceasingly alert or active

sleeplessly adverb

sleeplessness noun

Medical Definition

sleepless

adjective

sleep·​less ˈslē-pləs 

: not able to sleep : insomniac

sleeplessness noun