Definition of equilateral
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.
Origin and Etymology of equilateral
Late Latin aequilateralis, from Latin aequi- + later-, latus side — more at lateral
First Known Use: 1570
EQUILATERAL Defined for Kids
Definition of equilateral for Students
: having all sides or faces equal <an equilateral triangle>
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