Pronunciation: /ˌi kwəˈlæ tər əl/ ?

A polygon whose sides are the same length is called equilateral.[1] 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 in manipulative 1 and drag them to change the figures. No matter how you change these figures, they remain equilateral.


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Manipulative 1: Equilateral figures. Created with GeoGebra.


  1. equilateral. http://wordnet.princeton.edu/. WordNet. Princeton University. (Accessed: 2011-01-08). http://wordnetweb.princeton.edu/perl/webwn?s=equilateral&sub=Search+WordNet&o2=&o0=1&o7=&o5=&o1=1&o6=&o4=&o3=&h=.
  2. Carol Vorderman. Math Dictionary , pg 38. DK CHILDREN, July 20, 2009.

More Information

  • McAdams, David. Equilateral Triangle. allmathwords.org. All Math Words Encyclopedia. Life is a Story Problem LLC. 2009-03-12. http://www.allmathwords.org/article.aspx?lang=en&id=Equilateral%20Triangle.
  • McAdams, David. Polygon. allmathwords.org. All Math Words Encyclopedia. Life is a Story Problem LLC. 2009-03-12. http://www.allmathwords.org/article.aspx?lang=en&id=Polygon.

Printed Resources

Cite this article as:

Equilateral. 2010-01-25. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/e/equilateral.html.


Image Credits

Revision History

2008-12-13: Added derivation of word from Latin (McAdams, David.)
2008-11-18: Changed manipulative to GeoGebra. Added sentence on polygons (McAdams, David.)
2008-07-16: Added vocabulary links (McAdams, David.)
2008-06-07: Corrected spelling (McAdams, David.)
2008-05-10: Initial version (McAdams, David.)

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