**The Collaborative International Dictionary of English v.0.48:**

Trigonometry \Trig`o*nom"e*try\, n.; pl. -tries. [Gr. ? a
triangle + -metry: cf. F. trigonom['e]trie. 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.
[1913 Webster]
2. A treatise in this science.
[1913 Webster]
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.
[1913 Webster]