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

Samson Waithaka plays a prince who promised to marry Mumbi, creating a love triangle. —Georg Szalai, HollywoodReporter, 4 Sep. 2025

For those living under a rock, the series revolved around the love triangle between human high schooler Bella Swan (Kristen Stewart); her vampire boyfriend, Edward Cullen (Robert Pattinson); and her werewolf friend, Jacob Black (Taylor Lautner). —Wesley Stenzel, Entertainment Weekly, 4 Sep. 2025

Twilight, The Vampire Diaries, The OC, Gossip Girl, One Tree Hill… love triangles (particularly between two brothers) were an integral part of our cultural diet. —Olivia Petter, Vogue, 2 Sep. 2025

Prada’s signature triangle motif, which harks back to the brand’s founder Mario Prada, is a recognizable element of the lineup. —Luisa Zargani, Footwear News, 2 Sep. 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