tri·​an·​gle | \ˈtrī-ˌaŋ-gəl \

Definition of triangle 

1 : a polygon having three sides — compare spherical triangle

2a : a percussion instrument consisting of a rod of steel bent into the form of a triangle open at one angle and sounded by striking with a small metal rod

b : a drafting instrument consisting of a thin flat right-angled triangle of wood or plastic with acute angles of 45 degrees or of 30 degrees and 60 degrees

3 : a situation in which one member of a couple is involved in a love affair with a third person

Illustration of triangle

Illustration of triangle

triangle 1: 1 equilateral, 2 acute, 3 obtuse, 4 scalene, 5 isosceles, 6 right triangle

Examples of triangle in a Sentence

She cut the sandwiches into triangles.

Recent Examples on the Web

Scientists also expect to explore the glacier’s grounding zone, planning to drill through 800 meters of ice to observe over several seasons where the triangle of ice, ocean, and rock meet. Paul Voosen, Science | AAAS, "U.S.-U.K. science armada to target vulnerable Antarctic ice sheet," 30 Apr. 2018 As concealer: Be sure to try one of Reneau's go-to techniques — draw on a triangle of color, starting at the outer corner of your eye, moving diagonally downwards toward your cheekbone, then back up to the inner corner of the eye, and blend. Melanie Rud Chadwick, Allure, "Exclusive: Too Faced's Super-Sized and Revamped Its Born This Way Concealer," 13 June 2018 This new opera by the composer George Benjamin and the playwright Martin Crimp centers on a love triangle inspired by the relationship between King Edward II of England and his courtier Piers Gaveston. Sara Aridi, New York Times, "What’s on TV Saturday: ‘The Tale’ and ‘From Here to Eternity’," 26 May 2018 Cut each waffle into 4 triangles just before serving. Anna Helm And Gabriella Vigoreaux, Country Living, "Rainbow Waffle Sandwiches," 22 May 2018 Playhouse Square Foundation owns the new Crowne Plaza, built in 1995 on the triangle of land at the intersection of Euclid Avenue and Huron Road E, across from the city's theater complex. Susan Glaser,, "Take a tour of Cleveland's new Crowne Plaza at Playhouse Square, formerly the Wyndham (photos)," 29 Apr. 2018 Allow several hours for the dough to chill before cutting into triangles and baking. Lisa Yockelson,, "Recipe: Lots of lemon flavor is baked into these plump, glazed walnut scones," 16 Apr. 2018 To serve: Cut the warm, pressed baguettes into triangles and arrange on a serving platter. Sarah Fritsche, San Francisco Chronicle, "Recipe: The Grilled Cheez Guy’s Nacho Guyz," 12 Apr. 2018 Much better was the Hamachi Zu sashimi ($9), consisting of a half-dozen pieces of yellowtail, thickly sliced into triangles, soaking in a citrusy ponzu sauce. Malcolm Mayhew, star-telegram, "Poke Stop sure-footed as it catches first wave of Hawaiian-dining trend in Fort Worth | Fort Worth Star-Telegram," 4 Apr. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'triangle.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of triangle

14th century, in the meaning defined at sense 1

History and Etymology for triangle

Middle English, from Anglo-French, from Latin triangulum, from neuter of triangulus triangular, from tri- + angulus angle

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Statistics for triangle

Last Updated

6 Nov 2018

Look-up Popularity

Time Traveler for triangle

The first known use of triangle was in the 14th century

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More Definitions for triangle



English Language Learners Definition of triangle

: a shape that is made up of three lines and three angles

: something that is shaped like a triangle

: a musical instrument that is made of a steel rod bent into the shape of a triangle and that you play by hitting with a metal rod


tri·​an·​gle | \ˈtrī-ˌaŋ-gəl \

Kids Definition of triangle

1 : a flat geometric figure that has three sides and three angles

2 : something that has three sides and three angles a triangle of land

3 : a musical instrument made of a steel rod bent in the shape of a triangle with one open angle


tri·​an·​gle | \ˈtrī-ˌaŋ-gəl \

Medical Definition of triangle 

: a three-sided region or space and especially an anatomical one — see anterior triangle, carotid triangle, femoral triangle, posterior triangle, suboccipital triangle

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Comments on triangle

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a private place of worship

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