Definition of triangle in English:

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Pronunciation: /ˈtrīˌaNGɡəl/


1A plane figure with three straight sides and three angles: an equilateral triangle
More example sentences
  • Cross-sections are in the shape of circles, ovals, squares, rectangles, equilateral triangles or regular polygons.
  • He tested this intuition using two-dimensional plane figures - the triangle, square, pentagon, etc. - but this didn't work.
  • The design radiates symmetrically from a central point and is constructed from a pattern of circles, equilateral triangles, squares, hexagons and/or six-pointed stars.
1.1A thing shaped like a triangle: a small triangle of grass
More example sentences
  • Here, the ligament is assumed to be formed on an enlarging triangle that maintains its shape during growth.
  • The ear ornaments in this collection are geometrically complex in design, combining squares, circles and triangles into single forms.
  • It was a white triangle with a red border and a black exclamation mark inside and had to be pasted on the windshield and the back window of the cars driven by inexperienced drivers.
1.2A situation involving three people or things, especially an emotional relationship involving a couple and a third person with whom one of them is involved.
Example sentences
  • In a triangle, the three relationships are interdependent; they are not three separate person-to-person dyads.
  • The third person in the triangle is receiving affection and intimacy that rightfully belongs to the spouse.
  • And nothing is quite so potent an activator of consciousness as a relationship triangle.
1.3A musical instrument consisting of a steel rod bent into a triangle and sounded by being struck with a small steel rod.
Example sentences
  • We were given drums, triangles, maracas and tambourines to experiment with.
  • As she lay trembling slightly for a long moment, not daring to breathe, she became aware of a faint humming, like the sound that a triangle makes after you strike it.
  • It was the first time I ever heard a recorded triangle that didn't sound false.
1.4A frame used to position the balls in pool and snooker.
Example sentences
  • He racked up a triangle of pool balls at the proper end of the table, and he began to practice his pool shots.
  • This trophy, made of Waterford Crystal and in the shape of a snooker frame triangle, is a new one because the previous cup was sponsored by a tobacco company and their link with sport ended two seasons ago.
  • Only the shape of the rack of balls is a triangle.
1.5North American A drawing instrument in the form of a right triangle.
Example sentences
  • Use a triangle to lay out the outline of the label, a vertical center line, and horizontal guidelines for the height of the lettering.
  • Use a triangle to line those up and see that they're at right angles, then draw across them using the grid ruler.
1.6 (triangles) historical A frame of three halberds joined at the top to which a soldier was bound for flogging.
Example sentences
  • Sage had screamed at every blow, but now hung unconscious from the triangle, while Cruttwell was taking his flogging in silence.
  • For a flogging, three halberds would be bound in an upright triangle, with a fourth tied horizontally across at chest height.


Late Middle English: from Old French triangle or Latin triangulum, neuter of triangulus 'three-cornered' (see tri-, angle1).

  • triad from mid 16th century:

    Triad meaning ‘set of three’ goes back to Greek tres ‘three’. The Chinese secret societies are called Triads from their Chinese name San Ho Hui which can be translated as ‘tripe union society’. Triangle (Late Middle English) comes from the same word. The eternal triangle of romance dates from the early 20th century. Trinitas is the Latin for ‘triad’ and the source of trinity (Middle English). The musical trio (early 18th century) comes from the Italian development of tres. Triple (Middle English) is from the same root; and tripod (early 17th century) is a three-footed device, from tri- ‘three’ podes ‘feet’. Trivet (Late Middle English) comes from the Latin form of the word.

For editors and proofreaders

Syllabification: tri·an·gle

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