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# equilateral

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## Definition of equilateral

1. 1 :  having all sides equal <an equilateral triangle> <an equilateral polygon> — see triangle illustration

2. 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.

## Origin and Etymology of equilateral

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

First Known Use: 1570

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## Definition of equilateral for Students

1. :  having all sides or faces equal <an equilateral triangle>

1. Spanish Central: Translation of equilateral

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