Any of several single-valued or multivalued functions that are inverses of the sine function. Symbol: arcsin, sin^(-1) [Wiktionary.] In mathematics, the inverse trigonometric functions (occasionally called cyclometric functions) are the inverse functions of the trigonometric functions (with suitably restricted domains). Specifically, they are the inverses of the sine, cosine, tangent, cotangent, secant, and cosecant functions. They are used to obtain an angle from any of the angle's trigonometric ratios. Inverse trigonometric functions are widely used in engineering, navigation, physics, and geometry. ... Etymology of the arc- prefix. When measuring in radians, an angle of θ radians will correspond to an arc whose length is rθ, where r is the radius of the circle. Thus, in the unit circle, "the arc whose cosine is x" is the same as "the angle whose cosine is x", because the measure of the length of the arc of the circle in radii is the same as the measurement of the angle in radians. [Inverse trigonometric functions. Wikipedia]