triangle
Americannoun
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triangles
plural
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a closed plane figure having three sides and three angles.
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a flat triangular piece, usually of plastic, with straight edges, used in connection with a T square for drawing perpendicular lines, geometric figures, etc.
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any three-cornered or three-sided figure, object, or piece.
a triangle of land.
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a musical percussion instrument that consists of a steel triangle, open at one corner, that is struck with a steel rod.
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a group of three; triad.
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a situation involving three persons, especially one in which two of them are in love with the third.
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Astronomy. Triangle, the constellation Triangulum.
noun
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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: 1/ 2 base × height
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any object shaped like a triangle
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any situation involving three parties or points of view See also eternal triangle
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music a percussion instrument consisting of a sonorous metal bar bent into a triangular shape, beaten with a metal stick
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a group of three
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Etymology
Origin of triangle
First recorded in 1350–1400; Middle English, from Latin triangulum, noun use of neuter of triangulus “three-cornered”, see tri-, angle 1
Explanation
A triangle is a flat shape with three sides and three angles, like a slice of pizza, a yield sign, or the Greek letter delta. If you look carefully, you'll notice triangles all around you! A triangle is a polygon, which is a closed shape like a square or a hexagon, but a triangle has only three sides. Wedges of pie and some tortilla chips are shaped like triangles. If you invite your crush to a movie and they bring a date, you have yourself a love triangle. Triangle comes from the Latin word triangulus, "three-cornered" or "having three angles," from the roots tri-, "three," and angulus, "angle or corner."
Vocabulary lists containing triangle
The ACT Math Test: Geometry, List 1
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Geometry - Introductory
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Geometry - Middle School
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
AstraZeneca AZN -2.12%decrease; red down pointing triangle said it is ending the Phase 3 trial of volrustomig plus chemotherapy for metastatic non-small-cell lung cancer.
From The Wall Street Journal ● Aug. 17, 2026
Burger King has lately been drawing diners at a swifter rate than both McDonald’s MCD 0.21%increase; up pointing triangle and Wendy’s WEN -0.12%decrease; down pointing triangle , and its restaurant sales are growing faster.
From The Wall Street Journal ● Aug. 17, 2026
Meanwhile Coach, which is Tapestry’s TPR 0.46%increase; up pointing triangle main handbag brand, increased sales by 14% last quarter.
From The Wall Street Journal ● Aug. 17, 2026
Other powerful and efficient models have emerged in China this summer, too, including ones from tech giant Alibaba and startups Z.ai and MiniMax 100 -12.69%decrease; down pointing triangle .
From The Wall Street Journal ● Aug. 16, 2026
Liyana wasn’t sure what you would call the burgundy triangle sitting straight up on top of his head.
From "Habibi" by Naomi Shihab Nye
Another young adult drama debuting later this year is “Minimum Wage,” which focuses on teens managing part-time jobs and love triangles.
From Los Angeles Times ● Aug. 14, 2026
The rotations of these wide triangles make it hard for opponents to know who they should be picking up.
From BBC ● Aug. 10, 2026
Burnham’s inheritance includes two triangles from hell, says Mujtaba Rahman, head of Europe for risk analysis firm Eurasia.
From The Wall Street Journal ● Jun. 24, 2026
For four points you can attach two equilateral triangles along an edge to make a diamond shape with five pairs of points the same distance from each other.
From Slate ● Jun. 22, 2026
I lie back on the grass, tucking my knees up into triangles.
From "Leah on the Offbeat" by Becky Albertalli
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
