noun
also trigonometric ratio
1. : a function (as the sine, cosine, tangent, cotangent, secant, or cosecant) of an arc or angle most simply expressed in terms of the ratios of pairs of sides of a right-angled triangle — called also circular function
2. : the inverse (as the arc sine, arc cosine, arc tangent, arc cotangent, arc secant, or arc cosecant) of a trigonometric function