definition of
[pi]

[1] #1 pi n. the ratio of the circumference to the diameter of a circle; approximately equal to 3.14159265358979323846.... wn

[2] #2 pi n. [private detective, PI, private eye, private investigator, operative, shamus, sherlock] someone who can be employed as a detective to collect information. wn

[3] #3 pi n. [principal investigator, PI] the scientist in charge of an experiment or research project. wn

[4] #4 pi n. the 16th letter of the Greek alphabet. wn

[5] #5 pi n. [protease inhibitor, PI] an antiviral drug used against HIV; interrupts HIV replication by binding and blocking HIV protease; often used in combination with other drugs. wn