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
Keep scrolling for more
Keep scrolling for more
Keep scrolling for more
Test Your Vocabulary
Slippery Words Quiz—Changing with the Times
- What is an earlier meaning of nice?

Can you spell these 10 commonly misspelled words?
TAKE THE QUIZ
A daily challenge for crossword fanatics.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridgedWords at Play
Ask the Editors
Word Games
Slippery Words Quiz—Changing with the Times
Do you know these earlier meanings of words?
Take the quizWords of Snow and Ice Quiz
A selection of words from the chillier parts of t...
Take the quizSpell It
Can you spell these 10 commonly misspelled words?
Take the quizWord Winder's CrossWinder Play the game
Share equilateral
Time Traveler for equilateral
The first known use of equilateral was in 1570
See more words from the same year