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

Derived 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

Japan’s Tokyo Electron 8035 10.16%increase; green up pointing triangle and Kioxia Holdings were last 10% and 8.0% higher, respectively.

From The Wall Street Journal • Jun. 12, 2026

Its latest run began in 2011, when the off-road vehicle maker Polaris PII 1.87%increase; green up pointing triangle bought it from a private-equity firm.

From The Wall Street Journal • Jun. 12, 2026

Unionized workers at a Michigan plant producing a key component for General Motors GM -5.21%decrease; down pointing triangle trucks have reached a tentative agreement for a new labor contract following a 10-day strike.

From The Wall Street Journal • Jun. 11, 2026

RH RH 7.15%increase; up pointing triangle bumped up its revenue and margin forecast for the year as it expects a boost from a new venture focused on luxury home furnishings.

From The Wall Street Journal • Jun. 11, 2026

They sailed over the meadow in a triangle formation, three dark shadows on the grass.

From "The Secret History" by Donna Tartt

Related Words

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