trigonometry

Etymology

PIE word *tréyes From 1610s, from New Latin trigōnometria, from Ancient Greek τρίγωνον (trígōnon, “triangle”) + μέτρον (métron, “measure”). Equivalent to trigono- + -metry

noun

1. (geometry, mathematical analysis) The branch of mathematics that deals with the relationships between the sides and angles of (in particular) right-angled triangles, as represented by the trigonometric functions, and with calculations based on said relationships.
   Trigonometry emerged in the Hellenistic world during the 3rd century BCE from applications of geometry to astronomy; the Greeks focused on the calculation of chords, while mathematicians in India created the earliest known tables of values for trigonometric functions such as sine.
   Historically, trigonometry has been applied in areas such as geodesy, surveying, celestial mechanics and navigation.
   Trigonometry was originally the science which treated only of the sides and angles of plane and spherical triangles; but it has been recently extended so as to include the analytic treatment of all theorems involving the consideration of angular magnitudes. 1892, Edward Albert Bowser, A Treatise on Plane and Spherical Trigonometry, D. C. Heath & Co., page 1
   In fact, the earliest practical uses of trigonometry were in the fields of astronomy and hence navigation. 2013, Paul Abbott, Hugh Neill, Trigonometry: A Complete Introduction, Hachette, unnumbered page
   The properties of these new trigonometries and identities flowing from the definitions are then developed. The trigonometries derived from these generalizations will be jointly termed "The Fractional Trigonometry." 2016, Carl F. Lorenzo, Tom T. Hartley, The Fractional Trigonometry, Wiley, page 8