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

There’s a predictable love triangle, the betrayal that explains the corrosive relationship between the lion brothers and Biblical undertones that cast and recast the roles of Adam and Eve as well as Cain and Abel. —Lovia Gyarkye, The Hollywood Reporter, 17 Dec. 2024

Walking under a ladder: This superstition stems from the idea that walking under a ladder disrupts the triangle, a symbol of life, and invites misfortune. —Brandi D. Addison, Austin American-Statesman, 13 Dec. 2024

While there are beautiful ways to roll and fold napkins in a napkin ring, a simple triangle fold with a napkin ring around it is quick and looks stunning. $28 at Dillards.com Chic Glasses Everyone deserves to sip their beverage of choice from a special glass. —Tessa Cooper, Southern Living, 12 Dec. 2024

The upside-down triangle has become a symbol of violent resistance to Israel, according to the Anti-Defamation League. —Jake Tapper, CNN, 9 Dec. 2024

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

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