PI  
—abbreviation for  
1.  Philippine Islands 
2.  private investigator 
pi (pī)
n. pl. pis
Symbol π The 16th letter of the greek alphabet.
pI (pē'ī')
n.
The pH value for the isoelectric point of a given substance in solution.
pi (pī) Pronunciation Key
An irrational number that has a numerical value of 3.14159265358979... and is represented by the symbol π. It expresses the ratio of the circumference to the diameter of a circle and appears in many mathematical expressions. 
The irrational number obtained by dividing the length of the diameter of a circle into its circumference. Pi is approximately 3.1416. The sign for pi is π.
pi Pali 
Pi inorganic phosphate 
PI

PIS psychiatric information services 