[ ee-kwuh-lat-er-uh l, ek-wuh- ]
/ ˌi kwəˈlæt ər əl, ˌɛk wə- /


having all the sides equal: an equilateral triangle.


a figure having all its sides equal.
a side equivalent, or equal, to others.

Nearby words

  1. equicaloric,
  2. equid,
  3. equidistance,
  4. equidistant,
  5. equiform,
  6. equilateral hyperbola,
  7. equilateralism,
  8. equilibrant,
  9. equilibrate,
  10. equilibration

Origin of equilateral

From the Late Latin word aequilaterālis, dating back to 1560–70. See equi-, lateral

Related forms
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for equilateral

British Dictionary definitions for equilateral


/ (ˌiːkwɪˈlætərəl) /


having all sides of equal lengthan equilateral triangle


a geometric figure having all its sides of equal length
a side that is equal in length to other sides
Derived Formsequilaterally, adverb

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for equilateral



1560s, from Late Latin aequilateralis, from aequi- (see equal (adj.)) + lateralis (see lateral).

Online Etymology Dictionary, © 2010 Douglas Harper

Science definitions for equilateral


[ ē′kwə-lătər-əl ]

Having all sides of equal length, as a triangle that is neither scalene nor isosceles.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.