SINCE 1828

An Encyclopædia Britannica Company

boundary layer

noun

Definition of boundary layer

: a region of fluid (such as air) moving relative to a nearby surface (such as that of an airplane wing) that is slowed by the viscosity of the fluid and its adhesion to the surface

First Known Use of boundary layer

1921

Learn More about boundary layer

Britannica.com: Encyclopedia article about boundary layer

Seen and Heard

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

show

WORD OF THE DAY

akimbo

play

set in a bent position

Words at Play

alt-59775cb5d7779

Words We're Watching: 'Aquafaba'

Don't dump out the bean water just yet...

Words About Word Play

Don't just eat your words—play with them!

alt-596f95fe451e7

'Drought' & 'Drouth' Take Us Back In Time

A variant spelling with a long history

alt-59721dd897313

The 'Best' Way to Sign Off On An E-mail

Give them your best

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

The Emoji Quiz

Think you’re an emoji 👓 expert? Let’s see 🤔

Take the quiz

A Game of Thrones Word Quiz

In the Game of Thrones quiz, you learn some new vocabulary. (It’s quite safe, really. You will not die.)

Take the quiz

True or False?

Test your knowledge - and maybe learn something along the way.

Take the quiz

Syn City

Build a city of skyscrapers—one synonym at a time.

Play the game