Merriam-Webster Online Dictionary
triangle (noun)1.
a polygon having three sides - compare spherical triangle
2.
a) a percussion instrument consisting of a rod of steel bent into the form of a triangle open at one angle and sounded by striking with a small metal rod
b) a drafting instrument consisting of a thin flat right-angled triangle of wood or plastic with acute angles of 45 degrees or of 30 degrees and 60 degrees
3.
a situation in which one member of a couple is involved in a love affair with a third person
