The Collaborative International Dictionary of English v.0.48:

Pi \Pi\ (p[=e]` [imac]"), n. (Chem.)
   The inorganic orthophoshate ion; -- a symbol used in
   biochemistry. [acronym]
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Pi \Pi\ (p[imac]), n. [See Pica, Pie magpie, service-book.]
   (Print.)
   A mass of type confusedly mixed or unsorted. [Written also
   pie.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pi \Pi\ (p[imac]), n. [Gr. pi^.]
   1. A Greek letter ([Pi], [pi]) corresponding to the Roman
      letter P.
      [Webster 1913 Suppl.]

   2. Specifically: (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 twenty decimal places, is
      3.14159265358979323846 (see note). The number pi is an
      irrational number, i.e. it cannot be expressed as the
      quotient of two integers. It is also a transcendental
      number, i.e. it cannot be expressed as a root of an
      algebraic equation with a finite number of terms; 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.
      [Webster 1913 Suppl. +PJC]

   Note: The first 1000 decimal digits of the number pi are as
         displayed below.
         The digits are arranged as five sets of ten digits per
         line in twenty lines, proceeding left to right in each
         line.
         3.
         1415926535 8979323846 2643383279 5028841971 6939937510
         5820974944 5923078164 0628620899 8628034825 3421170679
         8214808651 3282306647 0938446095 5058223172 5359408128
         4811174502 8410270193 8521105559 6446229489 5493038196
         4428810975 6659334461 2847564823 3786783165 2712019091
         4564856692 3460348610 4543266482 1339360726 0249141273
         7245870066 0631558817 4881520920 9628292540 9171536436
         7892590360 0113305305 4882046652 1384146951 9415116094
         3305727036 5759591953 0921861173 8193261179 3105118548
         0744623799 6274956735 1885752724 8912279381 8301194912
         9833673362 4406566430 8602139494 6395224737 1907021798
         6094370277 0539217176 2931767523 8467481846 7669405132
         0005681271 4526356082 7785771342 7577896091 7363717872
         1468440901 2249534301 4654958537 1050792279 6892589235
         4201995611 2129021960 8640344181 5981362977 4771309960
         5187072113 4999999837 2978049951 0597317328 1609631859
         5024459455 3469083026 4252230825 3344685035 2619311881
         7101000313 7838752886 5875332083 8142061717 7669147303
         5982534904 2875546873 1159562863 8823537875 9375195778
         1857780532 1712268066 1300192787 6611195909 2164201989
         [Webster 1913 Suppl. +PJC]

The Collaborative International Dictionary of English v.0.48:

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.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

pi
    n 1: the ratio of the circumference to the diameter of a circle;
         approximately equal to 3.14159265358979323846...
    2: someone who can be employed as a detective to collect
       information [syn: private detective, PI, private eye,
       private investigator, operative, shamus, sherlock]
    3: the scientist in charge of an experiment or research project
       [syn: principal investigator, PI]
    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,
       PI]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "pi":
   ascender, back, ball up, bastard type, beard, belly, bevel,
   black letter, body, bollix up, cap, capital, case, compose,
   confound, confuse, counter, descender, em, en, face,
   fat-faced type, feet, font, foul up, fumble, garble, groove,
   impose, italic, jumble, justify, letter, ligature, logotype,
   lower case, majuscule, make up, minuscule, mix up, muck up, muddle,
   nick, overrun, pi a form, pica, play hob with, point, print,
   riffle, roman, sans serif, scramble, screw up, script, set,
   set in print, shank, shoulder, shuffle, small cap, small capital,
   snafu, snarl up, stamp, stem, tumble, type, type body, type class,
   type lice, typecase, typeface, typefounders, typefoundry,
   upper case



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

PI
       Placement and Interconnect [system] (VLSI, MIT)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

PI
       Portable Interceptor (CORBA)


The Free On-line Dictionary of Computing (30 December 2018):

PI

    An interface between Prolog application
   programs 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).  PI 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)


The Free On-line Dictionary of Computing (30 December 2018):

pi

   1.  The greek lower-case letter P.

   2.  The mathematical constant that is the
   circumference of a circle divided by its diameter.  Pi is written
   as the greek character pi.

   Some have suggested that pi is the wrong choice and a better
   constant to describe the geometry of circles would have been 2*pi,
   for which they have proposed the name tau.  Most practising
   mathematicians think this is silly.  The xkcd comic strip
   proposed (http://xkcd.com/1292/) a compromise between pi and
   tau, namely 1.5*pi or "pau".

   (2013-12-09)