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

Some of our favorite pieces are the result of collaborations with designers like Daniel Arsham, such as this triangle Landshapes knob that looks like something out of a sci-fi movie. — Lori Keong, Architectural Digest, 10 Sep. 2026

But arguably the Bertolucci film that might have spoken the loudest to that generation, 2003’s The Dreamers — a Jules et Jim-like romantic triangle set against the 1968 Paris student riots — is dispensed with in a brief clip or two, sans commentary. — David Rooney, HollywoodReporter, 9 Sep. 2026

But when one of his subscribers (Mizuhara) lures him to Japan to sell the rare jeans, he gets tangled in a love triangle and runs afoul of the yakuza. — Angelique Jackson, Variety, 9 Sep. 2026

Swapping all three is equivalent to rotating the triangle by 120 degrees clockwise or counterclockwise. — Quanta Magazine, 9 Sep. 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

• acute triangle
• equilateral triangle
• isosceles triangle
• obtuse 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