triangle

American  

[trahy-ang-guhl] / ˈtraɪˌæŋ gəl /

noun

1. a closed plane figure having three sides and three angles.

2. a flat triangular piece, usually of plastic, with straight edges, used in connection with a T square for drawing perpendicular lines, geometric figures, etc.

3. any three-cornered or three-sided figure, object, or piece.

   a triangle of land.

4. a musical percussion instrument that consists of a steel triangle, open at one corner, that is struck with a steel rod.

5. a group of three; triad.

6. a situation involving three persons, especially one in which two of them are in love with the third.

7. Astronomy. Triangle, the constellation Triangulum.

---

triangle British  

/ ˈtraɪˌæŋɡəl /

noun

1. geometry a three-sided polygon that can be classified by angle, as in an acute triangle, or by side, as in an equilateral triangle. Sum of interior angles: 180°; area: 1/ 2 base × height

2. any object shaped like a triangle

3. any situation involving three parties or points of view See also eternal triangle

4. music a percussion instrument consisting of a sonorous metal bar bent into a triangular shape, beaten with a metal stick

5. a group of three

---

triangle Scientific  

/ trī′ăng′gəl /

1. A closed geometric figure consisting of three sides.

---

triangle Idioms  

1. see eternal triangle.

---

Other Word Forms

• triangled
  adjective

Etymology

Origin of triangle

First recorded in 1350–1400; Middle English, from Latin triangulum, noun use of neuter of triangulus “three-cornered”, see tri-, angle ¹

Explanation

A triangle is a flat shape with three sides and three angles, like a slice of pizza, a yield sign, or the Greek letter delta. If you look carefully, you'll notice triangles all around you! A triangle is a polygon, which is a closed shape like a square or a hexagon, but a triangle has only three sides. Wedges of pie and some tortilla chips are shaped like triangles. If you invite your crush to a movie and they bring a date, you have yourself a love triangle. Triangle comes from the Latin word triangulus, "three-cornered" or "having three angles," from the roots tri-, "three," and angulus, "angle or corner."

Example Sentences

Appeared in the April 11, 2026, print edition as 'A Sizzling Love Triangle'.

From The Wall Street Journal • Apr. 10, 2026

Antler’s investments include AI telehealth and care platform Triangle Health, fitness platform Sweatpals and tracking software for delivery services company Doorstep.ai.

From The Wall Street Journal • Jan. 5, 2026

The new owner of the marble-clad property on the edge of the city’s prestigious Golden Triangle is Ashkenazy Acquisition Corp., a private real estate investment firm owned by Ben Ashkenazy.

From Los Angeles Times • Dec. 30, 2025

But the Falkirk Triangle is not the only UFO mystery to come from that period.

From BBC • Aug. 2, 2025

This has not been found to agree with experience, unless that turns out to be the explanation for the people who are supposed to have disappeared in the Bermuda Triangle!

From "A Brief History of Time: And Other Essays" by Stephen Hawking

Related Words

• adultery
• affair
• courtship
• dalliance
• devotion
• fling
• flirtation
• infidelity
• involvement
• liaison
• love
• passion
• relationship
• tryst