SINCE 1828

An Encyclopædia Britannica Company

calcium oxide

noun

Definition of calcium oxide

: a caustic solid CaO that is white when pure and that is the chief constituent of lime

See calcium oxide defined for kids

First Known Use of calcium oxide

1859

Learn More about calcium oxide

Britannica.com: Encyclopedia article about calcium oxide

Seen and Heard

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

show

WORD OF THE DAY

inhere

play

to be a fixed element or attribute

Words at Play

alt-597a00ef4b9d7

'Motif' vs 'Leitmotif'

A pattern emerges.

alt-5978b44edfb13

Our (Almost) Final Word on 'Penultimate'

The ultimate guide to using penultimate.

alt-5978cb55e8ba5

The Grammatical History of 'Awaken'/'Awoken'/'Awakened'

Or you can just go back to bed.

alt-59775cb5d7779

Words We're Watching: 'Aquafaba'

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

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

alt-597a99e699d07

July 2017 Words of the Day Quiz

Test your knowledge.

Take the quiz

The Emoji Quiz

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

Take the quiz

True or False?

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

Take the quiz

SCRABBLE® Sprint

SCRABBLE® Sprint

SCRABBLE® fans, sharpen your skills!

Play the game