Merriam-Webster Logo
SINCE 1828
Menu
×

An Encyclopædia Britannica Company

plane of symmetry

See What's Trending Now See More Trending Words

Definition of plane of symmetry

1 : a plane through a crystal that divides the crystal into two parts that are mirror images of each other
2 : a vertical fore-and-aft plane that divides an airplane into symmetrical halves

There's more!

Love words? You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

  • More than 250,000 words that aren't in our free dictionary
  • Expanded definitions, etymologies, and usage notes
  • Advanced search features
  • Ad free!
Already a subscriber? Log in.

Seen and Heard

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

show hide

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

WORD OF THE DAY

loath

play

unwilling or reluctant

Get Word of the Day daily email!

TRENDING NOW

  1. charlatan 'faker or fraud'

  2. lowlife 'a person of low moral character'

  3. kakistocracy 'government by the worst people'

  4. slimeball 'a morally repulsive or odious person'

  5. salacious 'arousing or appealing to sexual desire'

SEE ALL

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Words at Play

alt-5ade0f1ca7a0c
'Complement' vs. 'Compliment'

The distinction is clear (now).

image236659401
Words from Letters in the Greek Alphabet

When English borrows from another alphabet

alt-5ada140ed3e28
'Preventive' or 'Preventative'?

Why not both?

alt-5ad8fc71357ed
Words We're Watching: 'Bluebeard,' the Verb

No, it's not a coiffure trend

Ask the Editors

image1760257654
2017 Word of the Year: Behind the Scenes

How we chose 'feminism'

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'

video-literally
Literally

How to use a word that (literally) drives some people nuts.

video-his-or-her
Is Singular 'They' a Better Choice?

The awkward case of 'his or her'

Word Games

image1926873504
Odd Habits and Quirks Quiz

Test your knowledge of strange human behaviors.

Take the quiz
cats-on-impossible-timber
More Confusing Words—Quiz

How many of these commonly confused words do you know?

Take the quiz
Name That Thing
Name That Thing

Test your visual vocabulary with our 10-question challenge!

Take the quiz
Bee Cubed
Bee Cubed

Listen to the words and spell through all three levels.

Play the game