[noun] [C] - a flat shape with three straight sidesan equilateral trianglean isosceles triangleSee picture: ShapesA triangle is also anything which has three straight sides.Which ear-rings did you buy in the end - the triangles or the circles?A triangle is also a musical instrument consisting of a thin metal bar bent into a triangle shape which is hit with a metal bar to make a sound.See picture: Percussion instrumentsTriangle is also US for setsquare.
TRIANGLE
Meaning of TRIANGLE in English
Cambridge English vocab. Кембриджский английский словарь. 2012