Triangle

(tri'ang-gl.) [L. triangulum; from tres, three, and angulus, an angle.] (Geom.) A figure of three sides and three angles. T. are either plane or spherical. A plane T. is contained under three right lines, and a spherical under three arcs belonging to great circles of the sphere. An Isosceles T. has two equal sides; and a scalene T. has all its sides unequal. Similar T. are those whose angles are equal, and corresponding sides proportional.-(Mus.) A small triangular steel instrument, open at one of its angles, and played by striking it with a short bar of the same metal. [s. 906]