Pronunciation: /ˌi.kwəˈlæ.tər.əl/ Explain

A polygon whose sides are the same length is called equilateral.[2] The most commonly used equilateral polygon is the equilateral triangle. An equilateral quadrilateral is a parallelogram with equal sides. If the adjacent sides of an equilateral quadrilateral are perpendicular, the shape is a square. All regular polygons are equilateral.

The word equilateral is derived from Latin. Equi- is taken from the word aequus, meaning 'equal'. -lateral is taken from the word lateralis, meaning 'of the side'.


Click on the blue points and drag them to change the figure.

The sides on these figures are always the same size, are always equilateral.
Manipulative 1 - Equilateral Created with GeoGebra.


  1. McAdams, David E.. All Math Words Dictionary, equilateral. 2nd Classroom edition 20150108-4799968. pg 71. Life is a Story Problem LLC. January 8, 2015. Buy the book
  2. Carol Vorderman. Math Dictionary. pg 38. DK CHILDREN. July 20, 2009. Last Accessed 7/9/2018. Buy the book

More Information

  • McAdams, David E.. Equilateral Triangle. allmathwords.org. All Math Words Encyclopedia. Life is a Story Problem LLC. 3/12/2009. https://www.allmathwords.org/en/e/equilateraltriangle.html.

Cite this article as:

McAdams, David E. Equilateral. 12/21/2018. All Math Words Encyclopedia. Life is a Story Problem LLC. https://www.allmathwords.org/en/e/equilateral.html.

Image Credits

Revision History

12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)
7/5/2018: Removed broken links, updated license, implemented new markup, implemented new Geogebra protocol. (McAdams, David E.)
12/13/2008: Added derivation of word from Latin. (McAdams, David E.)
11/18/2008: Changed manipulative to GeoGebra. Added sentence on polygons (McAdams, David E.)
7/16/2008: Added vocabulary links. (McAdams, David E.)
6/7/2008: Corrected spelling. (McAdams, David E.)
5/10/2008: Initial version. (McAdams, David E.)

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