Definitions of pi:

• noun:   the 16th letter of the Greek alphabet
• noun:   the ratio of the circumference to the diameter of a circle
• noun:   an antiviral drug used against HIV; interrupts HIV replication by binding and blocking HIV protease; often used in combination with other drugs
• noun:   the scientist in charge of an experiment or research project
• noun:   someone who can be employed as a detective to collect information
• name:  A surname (very rare: popularity rank in the U.S.: #69127)