triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

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

• 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

When the lander opens onto the lunar surface, two rovers with mirrors will head in different directions, forming a five-kilometer triangle with the lander as the triangle’s third point. —Joseph Howlett, Scientific American, 8 Apr. 2026

The first clip, which THR can reveal here, teases the emotion, the intimacy, and the love triangle that audiences can expect from the series. —Georg Szalai, HollywoodReporter, 8 Apr. 2026

Off-screen, a complicated love triangle involving castmates Amanda Batula, Ciara Miller, and West Wilson has been unfolding across the internet in real time, adding another layer of intrigue to an already buzzy moment for the franchise. —Abby Montanez, Robb Report, 7 Apr. 2026

Topography, legacy a challenge to Canyon County’s water The area in question is a rough triangle bound by Lake Lowell and Lowell Road in the north, Idaho Highway 45 to the east and the Snake River to the south. —Mark Dee april 6, Idaho Statesman, 6 Apr. 2026

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

Phrases Containing triangle

• equilateral triangle
• isosceles triangle
• Pascal's triangle
• right-angled triangle
• right triangle
• spherical triangle
• triangle inequality

Rhymes for triangle

• angle
• bangle
• dangle
• jangle
• mangle
• strangle
• tangle
• wrangle
• disentangle
• entangle
• quadrangle
• untangle

Kids Definition

triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

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 

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