isosceles

American  

[ahy-sos-uh-leez] / aɪˈsɒs əˌliz /

adjective

1. (of a straight-sided plane figure) having two sides equal.

   an isosceles triangle; an isosceles trapezoid.

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isosceles British  

/ aɪˈsɒsɪˌliːz /

adjective

1. (of a triangle) having two sides of equal length

2. (of a trapezium) having the two nonparallel sides of equal length

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isosceles Scientific  

/ ī-sŏs′ə-lēz′ /

1. Of or relating to a geometric figure having at least two sides of equal length.

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Etymology

Origin of isosceles

1545–55; < Late Latin < Greek isoskelḗs with equal legs, equivalent to iso- iso- + skél ( os ) leg + -ēs adj. suffix

Explanation

In geometry, the word isosceles describes a triangle with two sides that are the exact same length. The angles across from each equal side are also the same in an isosceles triangle. Mathematicians use the term isosceles in two slightly different ways. The Greek mathematician Euclid defined an isosceles triangle as having exactly (and only) two equal sides. Modern geometry experts tend to say that a triangle is isosceles if at least two sides are equal — making an equilateral triangle (with three equal sides) also an isosceles triangle. The Greek root, isoskeles, means "with equal legs."

Example Sentences

A sort of isosceles triangle is formed, which will eventually collapse.

From Los Angeles Times • Apr. 4, 2024

He was so pretty, with his absurd curls and isosceles triangle of a nose and creamy brown face.

From New York Times • Feb. 28, 2019

A pyramid with height 5 units, and an isosceles triangular base with lengths of 6 units and 8 units, as seen here.

From Textbooks • Mar. 30, 2016

Arby’s Potato Cakes are lusty little isosceles triangles of pure crunch.

From Washington Post • Apr. 22, 2015

Greek letters move across the undersides of his eyelids: isosceles triangles, betas, sine curves.

From "All the Light We Cannot See" by Anthony Doerr