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[ahy-sos-uh-leez] /aɪˈsɒs əˌliz/
(of a straight-sided plane figure) having two sides equal:
an isosceles triangle; an isosceles trapezoid.
Origin of isosceles
1545-55; < Late Latin < Greek isoskelḗs with equal legs, equivalent to iso- iso- + skél(os) leg + -ēs adj. suffix Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for isosceles
  • Draw a circle in the center and then five lines from the center to the corners to create five isosceles triangles.
  • The figure shows a row of six solid white isosceles triangles.
  • Ask students to find two right angle isosceles triangles and predict what will be formed when they slide them together.
  • They will then find measures of the angles using the properties of isosceles and right triangles.
  • The atoms in a water molecule-two hydrogen and one oxygen-are arranged at the corners of an isosceles triangle.
  • When students work with tangrams, two congruent isosceles right triangles can be put together to compose a square.
  • FAll isosceles triangles are also equilateral triangles.
  • Most of the shapes of elementary geometry relate to the rectangle, and to the isosceles triangles generated by its diagonals.
  • The nose cone triangle can either be an isosceles or equilateral triangle.
British Dictionary definitions for isosceles


(of a triangle) having two sides of equal length
(of a trapezium) having the two nonparallel sides of equal length
Word Origin
C16: from Late Latin, from Greek isoskelēs, from iso- + skelos leg
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 isosceles

"having two equal sides," 1550s, from Late Latin isosceles, from Greek isoskeles "with equal sides," from isos "equal" (see iso-) + skelos "leg" (see scalene).

Online Etymology Dictionary, © 2010 Douglas Harper
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isosceles in Science
Of or relating to a geometric figure having at least two sides of equal length.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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