PI (3)

Pi (pī), n. [[Gr. πι̑.]] 1. 1. A Greek letter (Π, π) corresponding to the Roman letter P.
2. 2. Specif.: (Math.) The letter Π, π, as used to denote the number or quotient approximately expressing the ratio of the circumference of a circle to its diameter; also, the quotient or the ratio itself. The value of the quotient pi, to eight decimal places, is 3.14159265. The quotient pi cannot be expressed as a root of an algebraic equation; and from this fact follows the impossibility of the quadrature of the circle by purely algebraic processes, or by the aid of a ruler and compass.