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

And while a $3,000 mattress or a 22-step wind-down routine may look like the answer to your sleepless nights, the real answer is likely to be far more accessible, like keeping a consistent sleep-wake schedule and sharpening your sleep hygiene. —Sharon Brandwein, USA Today, 2 June 2026

According to the footage, what awaits Rhaenyra during her reign are fearful subjects, conniving enemies, sleepless nights and plenty of anguish. —Tracy Brown, Los Angeles Times, 29 May 2026

Night sweats, sleepless nights, brain fog; the search for relief has driven some to get creative in the drugstore aisle, combining daily antihistamines like Allegra or Claritin with antacids like Pepcid AC. —Helen Carefoot, Flow Space, 29 May 2026

There have been plenty of sleepless nights for Betts so far this season. —Katie Woo, New York Times, 27 May 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