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 bottom three stars can then be used to point the way to the Andromeda galaxy, by following an imaginary line from the 'base' of the stellar triangle up through the bright star Shedar and beyond, as shown in the finder map above. —Anthony Wood, Space.com, 28 Jan. 2026

Dressed all in black with his then-signature (pre-pandemic) mask, Bad Bunny stood atop the amplifier and brandished a Puerto Rican flag that included a light blue triangle, a version widely acknowledged as a pro-independence flag. —Julyssa Lopez, Rolling Stone, 26 Jan. 2026

Henie plays a young woman, caught in a love triangle, whose father has escaped from a concentration camp. —Natasha O'Neill, Vanity Fair, 26 Jan. 2026

Small bursts of red come again for the triangle formed at the third eyelet, as well as contrast stitching for the heel pull and the heel’s Air unit. —Ian Servantes, Footwear News, 26 Jan. 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