triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl How to pronounce triangle (audio)
1
: a polygon having three sides compare spherical triangle
2
a
: 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
  • 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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
The setting is mirrored in a tableau beneath the painting with the same table, Jello salad, and plate of white bread sandwich triangles. Chadd Scott, Forbes.com, 20 Aug. 2025 Venus will be visible as a bright 'morning star' shining approximately 5 degrees to the lower right of the lunar disk, while Jupiter will sit less than 10 degrees to the upper right of the moon, forming the highest point of the cosmic triangle. Anthony Wood, Space.com, 19 Aug. 2025 Indeed, triangles are the most basic polygon; any complex 3D shape can be broken down into a mesh of interconnected triangles. Dave Smith, Fortune, 19 Aug. 2025 Shaped like a triangle, the brush head can easily get to tight corners. Isabel Garcia, People.com, 17 Aug. 2025 See All Example Sentences for triangle

Word History

Etymology

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

First Known Use

14th century, in the meaning defined at sense 1

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

Browse Nearby Words

Cite this Entry

“Triangle.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/triangle. Accessed 29 Aug. 2025.

Kids Definition

triangle

noun
tri·​an·​gle ˈtrī-ˌaŋ-gəl How to pronounce triangle (audio)
1
: a figure that has three sides and three angles : a polygon that has three sides
2
: a percussion instrument made of a steel rod bent into a triangle open at one corner which is played by striking with a metal rod
3
: a drafting instrument consisting of a thin flat right-angled triangle

Medical Definition

triangle

noun
tri·​an·​gle ˈtrī-ˌaŋ-gəl How to pronounce triangle (audio)
: a three-sided region or space and especially an anatomical one see anterior triangle, carotid triangle, femoral triangle, posterior triangle, suboccipital triangle

More from Merriam-Webster on triangle

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