triangle

Etymology

PIE word *tréyes From Middle English triangle, from Old French triangle, from Latin triangulum, noun use of adjective triangulus (“three-cornered, having three angles”), from trēs (“three”) + angulus (“corner, angle”).

noun

1. (geometry) A polygon with three sides and three angles.
   The wedge-shaped character was the triangle, the archaic Paleolithic sign of the vulva; the pubic triangle was at the end of the phallic stylus. 1981, William Irwin Thompson, The Time Falling Bodies Take to Light: Mythology, Sexuality and the Origins of Culture, London: Rider/Hutchinson & Co., page 22
2. (US, Canada) A set square.
3. (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. (cue sports) A triangular piece of equipment used for gathering the balls into the formation required by the game being played.
5. A love triangle.
   One of the writers' most pleasing inventions was to treat the triangle love story as comedy. 2009, Neil McDonald, Quadrant, November 2009, No. 461 (Volume LIII, Number 11), Quadrant Magazine Limited, page 104
6. (systemics) The structure of systems composed with three interrelated objects.
7. A draughtsman's square in the form of a right-angled triangle.
8. (historical, usually in the plural) A frame formed of three poles stuck in the ground and united at the top, to which people were bound when undergoing corporal punishment.
   But nothing is said as to what we are to do with the negro when we have cut him off from absolute dominion; we are not informed if we may spread him on the triangles as aforetime; 1868, “The Week”, in The Nation, volume 6, number 149
9. Any of various large papilionid butterflies of the genus Graphium.
10. (rail transport) A triangular formation of railway tracks, with a curve on at least one side.
    After turning on the triangle at Jeumont, we set off light engine back to Aulnoye. 1961 March, ""Balmore"", “Driving and firing modern French steam locomotives”, in Trains Illustrated, page 147