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

The $12.3 billion fund—a business-development company called FS KKR Capital FSK -1.00%decrease; red down pointing triangle —has been under pressure since last year, when it disclosed its largest investment was underwater.

From The Wall Street Journal • May 11, 2026

Apollo Global Management APO 4.23%increase; green up pointing triangle said this past week that gross returns on its direct origination funds that include investment-grade loans to companies were 0.5%, down from 2.6% a year ago.

From The Wall Street Journal • May 11, 2026

The South Africa-based telecommunications company—which is majority-owned by Vodafone Group VOD 1.43%increase; green up pointing triangle —raised its final dividend for the year ended March 31 by 21% to 4.05 rand a share.

From The Wall Street Journal • May 11, 2026

Apollo Global Management APO 4.23%increase; green up pointing triangle struck deals for two different live-events businesses as part of a plan to create a platform for in-person gatherings.

From The Wall Street Journal • May 11, 2026

The triangle in Figure 23 has a height of 8 and a base of 8; since the area of a triangle is half the base times the height, the area is 32.

From "Zero: The Biography of a Dangerous Idea" by Charles Seife

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