Webster's English Dictionary

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pi

1. pi \'pi-\ n [MGk, fr. Gk pei, of Sem origin; akin to Heb pe- pe] 1: the 
   16th letter of the Greek alphabet - symbol P or p  2a: the symbol p 
   denoting the ratio of the circumference of a circl e to its diameter 2b: 
   the ratio itself : a transcendental number having a value to eight de cimal 
   places of 3.14159265
2. pi n or pies [origin unknown] pl  1: type or type matter that is 
   spilled, mixed, or incorrectly distributed  2: a pi character or matrix 
3. pi vb or pied;  or pi.ing : to spill or throw (type or type matter) into 
   disorder  : to become pied