triangle Meaning, Definition & Usage

noun a three-sided polygon
trilateral; trigon.
noun something approximating the shape of a triangle
- the coastline of Chile and Argentina and Brazil forms two legs of a triangle
noun a small northern constellation near Perseus between Andromeda and Aries
Triangulum.
noun any of various triangular drafting instruments used to draw straight lines at specified angles
noun a percussion instrument consisting of a metal bar bent in the shape of an open triangle

L. triangulum, fr. triangulus triangular; tri- (see Tri-) + angulus angle: cf. F. triangle. See Angle a corner.

(Geom.) A figure bounded by three lines, and containing three angles. ✍ A triangle is either plane, spherical, or curvilinear, according as its sides are straight lines, or arcs of great circles of a sphere, or any curved lines whatever. A plane triangle is designated as scalene, isosceles, or equilateral, according as it has no two sides equal, two sides equal, or all sides equal; and also as right-angled, or oblique-angled, according as it has one right angle, or none; and oblique-angled triangle is either acute-angled, or obtuse-angled, according as all the angles are acute, or one of them obtuse. The terms scalene, isosceles, equilateral, right-angled, acute-angled, and obtuse-angled, are applied to spherical triangles in the same sense as to plane triangles.
(Mus.) An instrument of percussion, usually made of a rod of steel, bent into the form of a triangle, open at one angle, and sounded by being struck with a small metallic rod.
A draughtsman's square in the form of a right-angled triangle.
(Mus.) A kind of frame formed of three poles stuck in the ground and united at the top, to which soldiers were bound when undergoing corporal punishment, -- now disused.
(Astron.) (a) A small constellation situated between Aries and Andromeda. (b) A small constellation near the South Pole, containing three bright stars.