Inverse trigonometrical functions , ∨ Circular function Meaning, Definition & Usage

Definitions
  1. the lengths of arcs relative to the sines, tangents, etc. Thus, AB is the arc whose sine is BD, and (if the length of BD is x) is written sin -1x, and so of the other lines. See Trigonometrical function (below). Other transcendental functions are the exponential functions, the elliptic functions, the gamma functions, the theta functions, etc.

Webster 1913