equilateral

adjective

equi·​lat·​er·​al ˌē-kwə-ˈla-tə-rəl How to pronounce equilateral (audio)
ˌe-,
-ˈla-trəl
1
: having all sides equal
an equilateral triangle
an equilateral polygon
see triangle illustration
2
: having all the faces equal
an equilateral polyhedron

Did you know?

Since equi- means "equal", the meaning of equilateral is easy to guess from its roots. The word is mostly used in geometry. The standard polygons (many-sided geometrical shapes)—the pentagon, hexagon, octagon, etc.—are assumed to be equilateral if we don't say otherwise; an equilateral rectangle has the special name square. But triangles are particularly important, and many triangles are not equal-sided. The standard polyhedrons (many-sided solids) are also equilateral. Most common is the cube, all of whose sides are square. The tetrahedron has four triangular sides and thus is a pyramid with a triangular base, unlike the pyramids of Egypt with their square bases.

Examples of equilateral in a Sentence

Recent Examples on the Web Each Magna-Tile is a translucent geometric shape, and this set includes squares (four large, 50 small) and triangles (11 right, 20 equilateral, and 15 isosceles). Katrina Cossey, Parents, 12 July 2023 This substantial set comes with 100 pieces, including squares (large and small) and triangles (equilateral, right and isosceles). Jessica Hartshorn, Good Housekeeping, 19 Dec. 2022 Waldo has floppy ears shaped like perfect equilateral triangles and feet too big for his lanky body, which continues to grow. Gemma Tarlach, Discover Magazine, 25 Nov. 2014 The set includes 48 regular squares, eight large squares, eight thick-sided squares, eight squares that look like windowpanes, 16 small and 16 large equilateral triangles plus 16 isosceles triangles. Jessica Hartshorn, Good Housekeeping, 19 Dec. 2022 The equilateral cross with its legs bent at right angles is a millennia-old sacred symbol in Hinduism, Buddhism and Jainism that represents peace and good fortune. Arkansas Online, 28 Nov. 2022 The equilateral cross with its legs bent at right angles is a millennia-old sacred symbol in Hinduism, Buddhism, and Jainism that represents peace and good fortune. Deepa Bharath, BostonGlobe.com, 27 Nov. 2022 The equilateral cross with its legs bent at right angles is a millennia-old sacred symbol in Hinduism, Buddhism and Jainism that represents peace and good fortune, and was also used widely by Indigenous people worldwide in a similar vein. Deepa Bharath, Anchorage Daily News, 27 Nov. 2022 This bolson is the sole source of water for three sizable towns set on a nearly equilateral triangle about twenty-five miles apart. Anna Badkhen, Harper’s Magazine , 28 Sep. 2022

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'equilateral.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

Etymology

Late Latin aequilateralis, from Latin aequi- + later-, latus side — more at lateral

First Known Use

1570, in the meaning defined at sense 1

Time Traveler
The first known use of equilateral was in 1570

Dictionary Entries Near equilateral

Cite this Entry

“Equilateral.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/equilateral. Accessed 22 Apr. 2024.

Kids Definition

equilateral

adjective
equi·​lat·​er·​al ˌē-kwə-ˈlat-ə-rəl How to pronounce equilateral (audio)
ˌek-wə-,
-ˈla-trəl
: having all sides or faces equal
an equilateral triangle

More from Merriam-Webster on equilateral

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