1. n. (geometry) A polygon with three sides and three angles.
2. n. (US, Canada) A set square.
3. n. (music) A percussion instrument made by forming a metal rod into a triangular shape which is open at one angle. It is suspended from a string and hit with a metal bar to make a resonant sound.
4. n. (cue sports) A triangular piece of equipment used for gathering the balls into the formation required by the game being played.
5. n. A love triangle.
6. n. (systemics) The structure of systems composed with three interrelated objects.
7. n. A draughtsman's square in the form of a right-angled triangle.
8. n. (historical) A frame formed of three poles stuck in the ground and united at the top, to which soldiers were bound when undergoing corporal punishment.
