triangle

American  

[trahy-ang-guhl] / ˈtraɪˌæŋ gəl /

noun

1. a closed plane figure having three sides and three angles.

2. a flat triangular piece, usually of plastic, with straight edges, used in connection with a T square for drawing perpendicular lines, geometric figures, etc.

3. any three-cornered or three-sided figure, object, or piece.

   a triangle of land.

4. a musical percussion instrument that consists of a steel triangle, open at one corner, that is struck with a steel rod.

5. a group of three; triad.

6. a situation involving three persons, especially one in which two of them are in love with the third.

7. Astronomy. Triangle, the constellation Triangulum.

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triangle British  

/ ˈtraɪˌæŋɡəl /

noun

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: 1/ 2 base × height

2. any object shaped like a triangle

3. any situation involving three parties or points of view See also eternal triangle

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

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triangle Scientific  

/ trī′ăng′gəl /

1. A closed geometric figure consisting of three sides.

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triangle Idioms  

1. see eternal triangle.

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Other Word Forms

• triangled adjective

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."

Example Sentences

India’s Sun Pharmaceutical Industries 524715 -3.57%decrease; red down pointing triangle has agreed to acquire U.S.-listed healthcare company Organon OGN 30.93%increase; green up pointing triangle & Co. for an enterprise value of $11.75 billion.

From The Wall Street Journal • Apr. 27, 2026

Consumer-products company Procter & Gamble PG 2.46%increase; green up pointing triangle , which sells brands including Tide, Crest, Puffs and Pampers, reported sales growth of 3%, below what it considers a normal rate of 4%.

From The Wall Street Journal • Apr. 27, 2026

Shares in German wind-turbine maker Nordex NDX1 10.41%increase; green up pointing triangle hit a 24-year high after the company reported first-quarter earnings well-ahead of analyst expectations.

From The Wall Street Journal • Apr. 27, 2026

He said he could "distinctly" remember seeing a red triangle on the painting, which "has always been the symbol of Bass beer".

From BBC • Apr. 26, 2026

The triangle DadEmmaJennifer locks in on my hand reaching for the fork.

From "Wintergirls" by Laurie Halse Anderson

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