Source : Webster's Revised Unabridged Dictionary (1913)

Pi \Pi\ (p[imac]), n. [Gr. pi^.]
   1. A Greek letter ([Pi], [pi]) corresponding to the Roman
      letter {P}.

   2. Specif.: (Math.) The letter [Pi], [pi], 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.

Pi \Pi\, n. [See {Pica}, {Pie} magpie, service-book.] (Print.)
   A mass of type confusedly mixed or unsorted. [Written also
   {pie}.]

Pi \Pi\, v. t. [imp. & p. p. {Pied}; p. pr. & vb. n. {Pieing}.]
   (Print.)
   To put into a mixed and disordered condition, as type; to mix
   and disarrange the type of; as, to pi a form. [Written also
   {pie}.]

Source : WordNet®

pi
     n 1: the ratio of the circumference to the diameter of a circle
          [syn: {3.14159265358979323846...}]
     2: someone who can be employed as a detective to collect
        information [syn: {private detective}, {private eye}, {private
        investigator}, {operative}, {shamus}, {sherlock}]
     3: the scientist in charge of an experiment or research project
        [syn: {principal investigator}]
     4: the 16th letter of the Greek alphabet
     5: an antiviral drug used against HIV; interrupts HIV
        replication by binding and blocking HIV protease; often
        used in combination with other drugs [syn: {protease
        inhibitor}]

Source : Free On-Line Dictionary of Computing

PI
     
        An interface between {Prolog} {application program}s and the
        {X Window System} that aims to be independent from the
        {Prolog} {engine}, provided that it has a {Quintus} {foreign
        function} interface (e.g. {SICStus} and {YAP}).  It is mostly
        written in {Prolog} and is divided in two libraries: Edipo -
        the lower level interface to the {Xlib} functions; and
        Ytoolkit - the higher level user interface toolkit.
     
        {(ftp://ftp.ncc.up.pt/pub/prolog/ytoolkit.tar.Z)}.
     
        E-mail: Ze' Paulo Leal .
     
        (1993-03-02)