- a closed plane figure having three sides and three angles.
- a flat triangular piece, usually of plastic, with straight edges, used in connection with a T square for drawing perpendicular lines, geometric figures, etc.
- any three-cornered or three-sided figure, object, or piece: a triangle of land.
- a musical percussion instrument that consists of a steel triangle, open at one corner, that is struck with a steel rod.
- a group of three; triad.
- a situation involving three persons, especially one in which two of them are in love with the third.
- the constellation Triangulum.
- a three-sided polygon that can be classified by angle, as in an acute triangle, or by side, as in an equilateral triangle. Sum of interior angles: 180°; area: 1/2 base × height
- any object shaped like a triangle
- any situation involving three parties or points of view
- a percussion instrument consisting of a sonorous metal bar bent into a triangular shape, beaten with a metal stick
- a group of three
