equilateral

adjective equi·lat·er·al \ ˌē-kwə-ˈla-tə-rəl , ˌe- , -ˈla-trəl \
Updated on: 19 Nov 2017

Definition of equilateral

1 : having all sides equal
  • an equilateral triangle
  • an equilateral polygon
— see triangle illustration
2 : having all the faces equal
  • an equilateral polyhedron

Recent Examples of equilateral from the Web

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'equilateral.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Did You Know?

Since equi- means "equal", the meaning of equilateral is easy to guess from its roots. The word is mostly used in geometry. The standard polygons (many-sided geometrical shapes)—the pentagon, hexagon, octagon, etc.—are assumed to be equilateral if we don't say otherwise; an equilateral rectangle has the special name square. But triangles are particularly important, and many triangles are not equal-sided. The standard polyhedrons (many-sided solids) are also equilateral. Most common is the cube, all of whose sides are square. The tetrahedron has four triangular sides and thus is a pyramid with a triangular base, unlike the pyramids of Egypt with their square bases.

Origin and Etymology of equilateral

Late Latin aequilateralis, from Latin aequi- + later-, latus side — more at lateral

Other Mathematics and Statistics Terms



EQUILATERAL Defined for Kids

equilateral

adjective equi·lat·er·al \ ˌē-kwə-ˈla-tə-rəl , ˌe-kwə- \

Definition of equilateral for Students

: having all sides or faces equal
  • an equilateral triangle

Learn More about equilateral


Seen and Heard

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

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

an inference not connected logically

Get Word of the Day daily email!

Test Your Vocabulary

Find the Cousins

  • a-large-tree-with-many-branches
  • Which pair shares a common word ancestor?
True or False

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

TAKE THE QUIZ
Bee Cubed

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

TAKE THE QUIZ

Love words? Need even more definitions?

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