noun pl. trigonometries
the branch of mathematics that deals with the ratios between the sides of a right triangle with reference to either acute angle (trigonometric functions), the relations between these ratios, and the application of these facts in finding the unknown sides or angles of any triangle, as in surveying, navigation, engineering, etc.
Origin:
ModL trigonometria < Gr trigōnon, triangle (see trigon) + -metria, measurement (see -metry)