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

But after the gatherings wind down, Christian prepares himself for one of the uncomfortable, sleepless nights that jeopardize his health. —Jessica Oliva, Miami Herald, 10 Dec. 2025

In the throes of diaper changes, cluster feedings, and sleepless nights, a strict skincare routine might be the last thing on your mind—and that’s okay. —Alex Vance, Parents, 10 Dec. 2025

In 5 More Sleeps ‘til Christmas, Fallon pays homage to the excitement of sleepless nights fueled by anticipation. —Lex Goldstein, PEOPLE, 30 Nov. 2025

With more than two decades of entrepreneurship under her belt at Late July, Dawes had pushed through economic downturns and many sleepless nights. —Emma Burleigh, Fortune, 23 Nov. 2025

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