Origin: Gr. A triangle _ -metry: cf. F. Trigonometrie. See Trigon.
1. That branch of mathematics which treats of the relations of the sides and angles of triangles, which the methods of deducing from certain given parts other required parts, and also of the general relations which exist between the trigonometrical functions of arcs or angles.
2. A treatise in this science. Analytical trigonometry, that branch of trigonometry which treats of the relations and properties of the trigonometrical functions. Plane trigonometry, and spherical trigonometry, those branches of trigonometry in which its principles are applied to plane triangles and spherical triangles respectively.