Definition of triangle noun from the Oxford Advanced Learner's Dictionary

      

    triangle

     noun
    noun
    BrE BrE//ˈtraɪæŋɡl//
     
    ; NAmE NAmE//ˈtraɪæŋɡl//
     
    Musical instruments
     
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  1. 1   a flat shape with three straight sides and three angles; a thing in the shape of a triangle (British English) a right-angled triangle (North American English) a right triangle Cut the sandwiches into triangles.
  2. 2a simple musical instrument that consists of a long piece of metal bent into the shape of a triangle, that you hit with another piece of metal See related entries: Musical instruments
  3. 3a situation involving three people in a complicated relationship a love triangle see also eternal triangle
  4. 4(North American English) (British English set square) an instrument for drawing straight lines and angles, made from a flat piece of plastic or metal in the shape of a triangle with one angle of 90°
  5. Word Origin late Middle English: from Old French triangle or Latin triangulum, neuter of triangulus ‘three-cornered’ (see tri- and the noun angle).Extra examples I cut the sandwiches into triangles. Use your protractor to construct an equilateral triangle. a large region resembling an inverted triangle
See the Oxford Advanced American Dictionary entry: triangle