Definition of triangle in English:


Line breaks: tri|angle
Pronunciation: /ˈtrʌɪaŋɡ(ə)l


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 musical instrument consisting of a steel rod bent into a triangle and sounded by being struck with a small steel rod.
More 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.
1.3A frame used to position the pool balls in snooker and pool.
More 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.
1.4North American A drawing instrument in the form of a right-angled triangle.
More 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.
1.5 (triangles) historical A frame of three halberds joined at the top to which a soldier was bound for flogging.
More 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.
2 (also eternal triangle) An emotional relationship involving a couple and a third person with whom one of them is also involved.
More 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.
3A small brownish Eurasian moth of oak and beech woods.
  • Heterogenea asella, family Limacodidae
More example sentences
  • The Blue Triangle is an active butterfly moving quickly from flower to flower.
  • The Gold Triangle is a beautiful purple and yellow moth.


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

Definition of triangle in: