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

Outlander Outlander $20 $9 Amazon Diana Gabaldon’s historical fantasy novel (which was adapted into a six-season series now on Netflix) isn’t your average love triangle. —Jenna Ryu, SELF, 1 May 2025

The two will form a triangle with Aldebaran, the bright red giant star in Taurus, just below — but act quickly because the trio will promptly sink into the horizon. —Jamie Carter, Forbes.com, 28 Apr. 2025

Francis Ford Coppola goes kinky gothic delicious for this classic tale of the Prince of Darkness/Jonathan Harker/Mina love triangle featuring Gary Oldman, Keanu Reeves, and Winona Ryder as its leads. —Jordan Crucchiola, Vulture, 26 Apr. 2025

The show follows the love triangle between Belly Conklin (Lola Tung) and a pair of brothers, Jermiah (Casalegno) and Conrad Fisher (Christopher Briney), along with the growing pains of coming-of-age and the grief of losing a parent. —Madison E. Goldberg, People.com, 25 Apr. 2025

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