1. Also called circular function. a function of an angle, as sine or cosine, expressed as the ratio of the sides of a right triangle.
2. any function involving only trigonometric functions and constants.
3. the generalization of these to functions of real or complex numbers. Also called trig function (for defs. 1, 2).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.