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[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.
1560-70; < Late Latin aequilaterālis. See equi-, lateral
Related forms
equilaterally, adverb
nonequilateral, adjective
nonequilaterally, adverb
subequilateral, adjective
unequilateral, adjective
unequilaterally, adverb Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Examples from the web for equilateral
  • The design is based on equilateral triangles, with a core living room and kitchen area, and two wings.
  • Being an eccentric geek, he is having the island shape changed from a rough triangle to a perfect equilateral triangle.
  • Together, the three tunnels would form an equilateral triangle.
  • At the apex, that is, of an equilateral triangle formed by you and your two speakers.
  • Have the words equilateral, isosceles, and scalene written on labels placed on a mat on the floor.
  • Three toothpicks together makes an equilateral triangle.
  • In the other activity a ball rests in the middle of an equilateral triangle.
  • Discuss with your partner a definition of equilateral triangle.
  • Then add two counters to form an equilateral triangle as shown.
  • Then add three counters, again forming an equilateral triangle.
British Dictionary definitions for equilateral


having all sides of equal length: an equilateral triangle
a geometric figure having all its sides of equal length
a side that is equal in length to other sides
Derived Forms
equilaterally, 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
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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
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equilateral in Science
Having all sides of equal length, as a triangle that is neither scalene nor isosceles.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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