SINCE 1828

An Encyclopædia Britannica Company

REM sleep

noun

Definition of REM sleep

:a state of sleep that recurs cyclically several times during a normal period of sleep and that is characterized especially by increased neuronal activity of the forebrain and midbrain, depressed muscle tone, dreaming, and rapid eye movements — called also paradoxical sleep, rapid eye movement sleep; compare slow-wave sleep

See REM sleep defined for English-language learners

First Known Use of rem sleep

1963

REM SLEEP Defined for English Language Learners

REM sleep

noun

Definition of REM sleep for English Language Learners

: a stage of sleep during which you dream and your eyes make quick movements

Medical Dictionary

REM sleep

noun

medical Definition of REM sleep

:a state of sleep that recurs cyclically several times during a normal period of sleep and that is characterized by increased neuronal activity of the forebrain and midbrain, by depressed muscle tone, and especially in humans by dreaming, rapid eye movements, and vascular congestion of the sex organs — called also desynchronized sleep, paradoxical sleep, rapid eye movement sleep; compare slow-wave sleep

Seen and Heard

What made you want to look up REM sleep? Please tell us where you read or heard it (including the quote, if possible).

show

WORD OF THE DAY

yeasty

play

of yeast or being unsettled or frivolous

BROWSE DICTIONARY

Remsen

Remsen cooler

REM sleep

remuda

remunerable

Test Your Vocabulary

Merriam-Webster's New Words Quiz—Fall 2017 Edition!

Which of the following is a new sense of the word bunny?

How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

TAKE THE QUIZ

Word Winder's CrossWinder

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Words at Play

alt-59c52d6ee2f72

Breathing Life Into 'Inspire'

The word's origins are quite literal

alt-59c4207ecf106

Let's Talk 'Tea'

Spill it, sip it: just make it hot.

8 Words and Phrases from Boxing and Wrestling

Common terms that come from boxing and wrestling

alt-59c2960017c94

The Ambiguity of Pushing 'Up' and 'Back'

When you push a meeting, where does it go?

Ask the Editors

video-title-words-of-the-year-1066

Words of the Year: 1066

Or, Why Pig Meat is Called 'Pork' and Cow Meat is Called 'Beef'

How Often Is 'Biweekly'?

Don't get us started on 'bimonthly'

video-irregardless-grammar-peeve-blend-of-the-synonyms-irrespective-and-regardless

Irregardless

It is in fact a real word (but that doesn't mean you should use it).

video-moose-goose-weird-plurals

Weird Plurals

One goose, two geese. One moose, two... moose. What's up with that?

Word Games

young-plant-shoots

Merriam-Webster's New Words Quiz—Fall 2017 Edition!

You're going to have to memorize the dictionary again.

Take the quiz

stylized-drawing-of-woman-pole-vaulting-across-gap-to-get-trophy

Challenging Vocabulary Quiz Returns!

No tricks, just difficult words.

Take the quiz

How Strong Is Your Vocabulary?

How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Take the quiz

Word Winder's CrossWinder

Word Winder's CrossWinder

A game of winding words.

Play the game