Definition of "trigonometry"

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