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

The 2002 movie Rules of Attraction introduced a darker side to Van Der Beek, as Sean Bateman, a drug dealer and the younger brother of American Psycho’s Patrick Bateman, who is caught in a love triangle with a virgin and her bisexual ex-boyfriend. —Ale Russian, Rolling Stone, 11 Feb. 2026

Their uneasy dynamic fractures when the attorney embarks on a consuming affair with a younger woman, igniting a volatile love triangle that unleashes obsession, betrayal and a ruthless battle for control of the family fortune. —Matt Grobar, Deadline, 10 Feb. 2026

The truck had parked on the shoulder due to a mechanical failure, and had deployed emergency warning triangles behind the trailer before the crash. —Todd Feurer, CBS News, 10 Feb. 2026

Our fellow guests were all seated at garden tables, nibbling sandwiches cut into little triangles and sipping from fancy teacups. —Flora Stubbs, Travel + Leisure, 7 Feb. 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