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

After fleeing Afghanistan to Brazil with her parents and two sisters, a four-month journey over rugged mountains and through thick jungles, enduring hunger and cold, sleepless nights, brought them to America. —Santa Ana College, Oc Register, 30 Apr. 2026

There were a few sleepless nights for Brighton & Hove Albion CEO Paul Barber following a board meeting a couple of weeks ago. —Charlotte Harpur, New York Times, 29 Apr. 2026

Melatonin has long been framed as a low-risk solution for sleepless nights. —Allison Palmer, Sacbee.com, 16 Apr. 2026

And there are countless others balancing hospital shifts, therapy schedules, sleepless nights, and advocacy — quietly rewriting what family, work, and resilience look like. —Dr. Joseph D'orazio, CNBC, 9 Apr. 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