triangle

IPA/ˈtraɪæŋɡl/
KK[trˈaɪˌæŋɡəl]IPA/ˈtraɪæŋɡl/

triangle — noun

  • trianglesingular
  • trianglesplural

1. A two-dimensional shape that is made by connecting three points with straight li

1.nounintransitiveA2
Definition

A two-dimensional shape that is made by connecting three points with straight lines. Every triangle has three sides and three corners.

Example

The maths teacher asked Hao to measure each angle of the triangle on the board.

collocation: angle of a triangle / measure an angle

A red triangle on a road sign usually means drivers should slow down.

common use: triangle on road signs

Common collocations
  • equilateral triangle
  • isosceles triangle
  • right-angled triangle
  • sides of a triangle
  • area of a triangle
  • angles of a triangle
Synonyms

Grammar Patterns

triangle + of

Usage Note

In mathematics, triangles are named by their side lengths (equilateral, isosceles, scalene) or by their angles (acute, right-angled, obtuse).

Common Mistakes

A pyramid has triangle sides.
A pyramid has triangular sides.
The adjective 'triangular' describes the shape, not the noun 'triangle'.

2. An object, area, or piece of material whose outline looks roughly like a three-s

2.nounintransitiveB1
Definition

An object, area, or piece of material whose outline looks roughly like a three-sided figure, even though it may not be a mathematically perfect one.

Example

Elena cut the sandwich into a triangle and packed it for her lunch.

collocation: cut + [food] + into a triangle

Anjali grows herbs in a small triangle of land at the back of the garden.

collocation: a triangle of [land/space/area]

Common collocations
  • a triangle of land
  • a triangle of cheese
  • cut into a triangle
Synonyms
  • wedge

    suggests a thicker, three-dimensional triangular shape, often of food

  • delta

    used for triangular land formations at river mouths, but very specific to geography

Grammar Patterns

a triangle of + noun

Usage Note

Common in descriptions of geography, urban spaces, and food preparation. 'A triangle of X' is a frequent pattern.

Common Mistakes

She wore a triangle scarf.
She wore a triangular scarf.
Use 'triangular' (adjective) before a noun, not 'triangle'.

3. A small percussion instrument crafted from a slender steel rod that is curved in

3.nounintransitiveB1
Definition

A small percussion instrument crafted from a slender steel rod that is curved into a three-sided open form. A string holds the instrument while the player taps it with a thin metal beater, producing a clear, high-pitched ringing sound.

Example

In the school orchestra, Jude was responsible for playing the triangle.

collocation: play the triangle (instrument)

The triangle gives a bright clear ring when tapped with a thin metal rod.

sound description: high, clear note

Common collocations
  • play the triangle
  • strike the triangle
  • triangle player
  • the triangle rings
Synonyms

Grammar Patterns

play the triangle

strike the triangle

Usage Note

When referring to the instrument as a general type, native speakers say 'the triangle' (e.g., 'She plays the triangle').

Common Mistakes

He hit the triangle with a drumstick.
He struck the triangle with a small metal rod.
A triangle is played with a metal beater or rod, not a standard drumstick.

4. A flat drawing aid cut into a right-angled triangular form and crafted from plas

4.nounintransitiveB1
Definition

A flat drawing aid cut into a right-angled triangular form and crafted from plastic or metal. Students and designers use it to draw neat lines and to check or mark specific angles on paper.

Example

Lisa used a triangle to draw parallel lines across her graph paper.

collocation: use a triangle to draw [lines]

The architect kept a clear plastic triangle inside her pencil case.

Common collocations
  • use a triangle
  • plastic triangle
  • draw with a triangle
  • triangle and ruler
Synonyms
  • set square

    more common in British English; refers to the same tool

Grammar Patterns

use a triangle

draw with a triangle

Usage Note

Also called a 'set square' in British English. 'Triangle' is the more common term in American English classrooms.

Common Mistakes

Draw a 90-degree line using a square.
Draw a 90-degree line using a triangle / set square.
A 'square' in this context usually means a T-square or carpenter's square, not a triangular drafting tool.

5. A wooden or plastic rack shaped like a triangle, used to pack the balls tightly

5.nounintransitiveB2
Definition

A wooden or plastic rack shaped like a triangle, used to pack the balls tightly against one another before the opening shot in pool, snooker, or billiards.

Example

The player placed the triangle over the balls before starting the game of pool.

collocation: place the triangle over the balls

Tamar lifted the triangle away after the balls were set for the break shot.

collocation: lift the triangle away / set the balls

Common collocations
  • place the triangle
  • remove the triangle
  • pool triangle
  • triangle for billiards
Synonyms
  • rack

    shorter and more common among experienced players; refers to any shaped frame, not just triangles

Grammar Patterns

place the triangle over [the balls]

triangle + for [game]

Usage Note

Also called a 'rack' or 'pool rack'. 'Triangle' is the most descriptive term for beginners because it emphasises the shape.

Common Mistakes

He used the triangle to hit the balls.
He used the triangle to arrange the balls.
The triangle is only for setting up the balls before play; it is removed before anyone hits the cue ball.

6. A set of circumstances where three people are emotionally linked with each other

6.nounintransitiveB2
Definition

A set of circumstances where three people are emotionally linked with each other — most often, one person has romantic ties with two others, leading to difficult emotions and decisions.

Example

The film tells the story of a love triangle between two brothers and one woman.

collocation: love triangle between [three people]

Nadia wanted to avoid being caught in a triangle with her two best friends.

collocation: caught in a triangle

Common collocations
  • love triangle
  • a triangle between
  • caught in a love triangle
  • messy love triangle
Synonyms
  • love triangle

    the full standard phrase; 'triangle' alone is a shortened form

  • complicated relationship

    broader and less specific; can describe any difficult relationship, not just three-way involvement

Grammar Patterns

a love triangle + between [people]

Usage Note

Almost always appears as 'love triangle' rather than 'triangle' alone. 'Triangle' by itself can sound vague, so the full phrase is strongly preferred in both speech and writing.

Common Mistakes

The movie has a triangle couple.
The movie features a love triangle.
'Love triangle' is the fixed expression; 'triangle couple' is not natural English.
They are in a triangle relationship.
They are in a love triangle.
Use the fixed noun phrase; 'triangle relationship' sounds like a direct translation.

Word family

  • triangular
    adjectiveB1
  • triangulate
    verbC1
  • triangulation
    nounC1
  • triangularly
    adverbC2

Common collocations

Nouns

  • side of a triangle
  • angle of a triangle
  • shape of a triangle

Phrases

  • right-angled triangle
  • love triangle
  • equilateral triangle

Prepositions

  • in a triangle
  • into a triangle
  • of a triangle

Etymology

LatinOld FrenchEnglish

The word 'triangle' comes from Latin 'triangulum', which is made up of 'tri-' (meaning three) and 'angulum' (meaning corner or angle). It travelled into English through Old French 'triangle' during the Middle Ages. The idea of a three-angled shape has existed in mathematics since ancient times, but the word itself became common in English around the 14th century.