PI

pi (http://definr.com/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, 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