a closed plane figure having three sides and three angles.
a flat triangular piece, usually of plastic, with straight edges, used in connection with a T square for drawing perpendicular lines, geometric figures, etc.
any three-cornered or three-sided figure, object, or piece: a triangle of land.
a musical percussion instrument that consists of a steel triangle, open at one corner, that is struck with a steel rod.
a group of three; triad.
a situation involving three persons, especially one in which two of them are in love with the third.
(initial capital letter) Astronomy. the constellation Triangulum.

1350–1400; Middle English < Latin triangulum, noun use of neuter of triangulus three-cornered. See tri-, angle1

triangled, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
triangle (ˈtraɪˌæŋɡəl)
1.  geometry a three-sided polygon that can be classified by angle, as in an acute triangle, or by side, as in an equilateral triangle. Sum of interior angles: 180°; area: ½ base × height
2.  any object shaped like a triangle
3.  See also eternal triangle any situation involving three parties or points of view
4.  music a percussion instrument consisting of a sonorous metal bar bent into a triangular shape, beaten with a metal stick
5.  a group of three
[C14: from Latin triangulum (noun), from triangulus (adjective), from tri- + angulus corner]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

late 14c., from O.Fr. triangle (13c.), from L. triangulum "triangle," from neut. of adj. triangulus "three-cornered," from tri- "three" + angulus "corner, angle." Triangulation is recorded from 1818.
"In the huts of witches all the instruments and implements are triangular." ["Handwörterbuch des deutschen Aberglaubens"]
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

triangle tri·an·gle (trī'āng'gəl)
A three-sided area, space, or structure.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
triangle   (trī'āng'gəl)  Pronunciation Key 
A closed geometric figure consisting of three sides.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Idioms & Phrases


see eternal triangle.

The American Heritage® Dictionary of Idioms by Christine Ammer.
Copyright © 1997. Published by Houghton Mifflin.
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Example sentences
Each is organized as a clear hierarchy rather than as a balanced triangle.
Between these two lines lies a large, fish-rich triangle.
Press down to create a pouch in the end of the plastic triangle.
The hypotenuse of a right triangle is not always the shortest distance between
  the two points that define it.
Idioms & Phrases
Image for triangle
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