PI

noun

1. someone who can be employed as a detective to collect information and assist in criminal investigations
2. the ratio of the circumference to the diameter of a circle; approximately equal to 3.14159265358979323846 …
3. the scientist in charge of an experiment or research project
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