equilateral
adjective
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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
Sofia Celeste, Footwear News, 10 Apr. 2025
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
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Cite this Entry
“Equilateral.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/equilateral. Accessed 5 Jul. 2025.
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equilateral
adjective
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