Definitions
from The American Heritage® Dictionary of the English Language, 5th Edition.
 adjective Having all sides or faces equal.
 noun A side exactly equal to others.
 noun A geometric figure having all sides equal.
from The Century Dictionary.
 In geometry, having all the sides equal: as, an equilateral triangle.
 In zoology: Having the two sides equal: said of surfaces which can be divided into two parts of the same form by a longitudinal median line.
 Having all the sides equal.
 Having all the convolutions of the shell in one plane: said chiefly of foraminifers.
 noun A figure having all its sides equal.
from the GNU version of the Collaborative International Dictionary of English.
 adjective Having all the sides equal
 adjective (Geom.) one whose axes are equal.
 adjective (Zoöl.) one in which a transverse line drawn through the apex of the umbo bisects the valve, or divides it into two equal and symmetrical parts.
 adjective applied to two figures, when every side of the one has its equal among the sides of the other.
 noun A side exactly corresponding, or equal, to others; also, a figure of equal sides.
from Wiktionary, Creative Commons Attribution/ShareAlike License.
 adjective geometry Referring to a
polygon all of whose sides are of equal length. Not necessarily aregular polygon since theangles can still differ (a regular polygon would also beequiangular ).  noun An
equilateral triangle
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
 noun a figure whose sides are all equal
 adjective having all sides or faces equal
Etymologies
Sorry, no etymologies found.
Examples

Ensure that the octagon is equilateral, meaning all sides on the ground have the same length.

a tiny mining company working claims in the remote "equilateral" cluster of asteroids far out in Jupiter's orbit.

For example, three Woolworths sites around Birmingham form an exact equilateral triangle (Wolverhampton, Lichfield and Birmingham stores) and if the base of the triangle is extended, it forms a 173.8 mile line linking the Conway and Luton stores.

From the moment that grand trine appeared in the sky—an equilateral triangle like the great pyramids—it was our turn to clean house.

Richardson, Taylor and Tomlinson are scattered, forming a sort of equilateral triangle.

How can anyone say that a scalene and an equilateral are really the same "kind"!

From the moment that grand trine appeared in the sky—an equilateral triangle like the great pyramids—it was our turn to clean house.

For example, if you enter 1, 3, 6, 10, 15, the server will tell you that is sequence A000217, the triangular numbers (these are the number of objects that can form an equilateral triangle like the standard arrangement of bowling pins.)
An Important AT&T Legacy Finds a New Home « Steve Wildstrom on Tech

It happened that the Lancashire Queen, the shore at Turner's Shipyard, and the Solano Wharf were the corners of a big equilateral triangle.

Obtained by the rotation of 60 ° of two equilateral triangles superimposed and spaced in height, the form appears simple but at the same time full of spatial complexity.
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