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”, 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

CarMax KMX 5.05%increase; green up pointing triangle swung to a fourth-quarter loss as it implements a turnaround strategy that has included price cuts to reestablish its place in the used-car market.

From The Wall Street Journal • Apr. 14, 2026

SYDNEY—Australia’s Qantas QAN -0.83%decrease; red down pointing triangle Airways said its near-term jet fuel bill would be up to 32% more than previously anticipated, as the Iran conflict hits profitability in global aviation.

From The Wall Street Journal • Apr. 14, 2026

A bullish ascending triangle pattern has taken shape.

From Barron's • Apr. 13, 2026

Conagra CAG -2.38%decrease; red down pointing triangle Brands has tapped veteran consumer-products executive John Brase to replace Sean Connolly as president and chief executive of the food maker, effective June 1.

From The Wall Street Journal • Apr. 13, 2026

The waving man at the peak of the right triangle is the climax of this mood of rising hope and advancing motion.

From "The Annotated Mona Lisa" by Carol Strickland and John Boswell

Related Words

• adultery
• affair
• courtship
• dalliance
• devotion
• fling
• flirtation
• infidelity
• involvement
• liaison
• love
• passion
• relationship
• tryst