[count] a shape that is made up of three lines and three angles - see picture at geometry; see also equilateral triangle, isosceles triangle, right triangle

something that is shaped like a triangle

a musical instrument that is made of a steel rod bent into the shape of a triangle and that you play by hitting with a metal rod

a situation in which one member of a couple is involved in a romantic or sexual relationship with another person

US :a usually plastic or metal device that is shaped like a triangle and used for drawing straight lines and angles - called also (Brit) set square