Definition of sleepless
1
: not able to sleep
lay sleepless with fever
2
: affording no sleep
sleepless nights
3
: unceasingly active or operative
sleepless casinos
Buying Guide
Our Reviews team has selected the best sleep masks.
Test Your Vocabulary
Name That Color
-
- Name that color:

Test your knowledge - and maybe learn something along the way.
TAKE THE QUIZ
A daily challenge for crossword fanatics.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridged
Share sleepless
Time Traveler for sleepless
The first known use of sleepless was in the 15th century
See more words from the same century