- a function of an angle, as sine or cosine, expressed as the ratio of the sides of a right triangle.
- any function involving only trigonometric functions and constants.
- the generalization of these to functions of real or complex numbers.
- any of a group of functions of an angle expressed as a ratio of two of the sides of a right-angled triangle containing the angle. The group includes sine, cosine, tangent, secant, cosecant, and cotangent
- any function containing only sines, cosines, etc, and constants
