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:
Norsk Hydro NHY -0.91%decrease; red down pointing triangle said it expects a further financial hit in the fourth quarter following gas supply challenges at its alumina refinery in Brazil.
From The Wall Street Journal ● Oct. 6, 2026
Before he became Disney’s DIS 1.39%increase; up pointing triangle top lawyer, Horacio Gutiérrez faced powerful adversaries, defending Microsoft in its antitrust fights and taking on Apple while at Spotify.
From The Wall Street Journal ● Oct. 6, 2026
Ithaca Energy ITH 2.76%increase; green up pointing triangle agreed to buy a portfolio of offshore oil projects from Canada’s Suncor Energy SU 0.87%increase; up pointing triangle for up to $1.11 billion.
From The Wall Street Journal ● Oct. 5, 2026
A major Mattel MAT 5.11%increase; up pointing triangle shareholder is calling for the toymaker to explore strategic alternatives, as the company deals with a sliding stock and now a chief-executive transition.
From The Wall Street Journal ● Oct. 5, 2026
As you can see, making smaller and smaller rectangles—whose widths, denoted by the symbol Δx, go to zero—makes the value closer and closer to 32, the true value for the area of the triangle.
From "Zero: The Biography of a Dangerous Idea" by Charles Seife
The triangles still behave like ordinary triangles, and the parallel lines still behave like parallel lines.
From Science Daily ● Sep. 28, 2026
Small triangles would behave almost exactly as Euclid predicted, and short parallel paths would not noticeably converge.
From Science Daily ● Sep. 28, 2026
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
Positional rotations in the wide triangles for Tuchel were supposed to be the key attacking tactic England were to lean on throughout the tournament.
From BBC ● Jul. 12, 2026
Instead of the diamond shapes on Pond, there were aggressive triangles and zigzags on this one.
From "Healer of the Water Monster" by Brian Young
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.
