TRIGONOM'ETRY, noun [Gr. a triangle, and to measure.] The measuring of triangles; the science of determining the sides and angles of triangles, by means of certain parts which are given. When this science is applied to the solution of plane triangles, it is called plane trigonometry; when its application is to spherical triangles, it is called spherical trigonometry
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI