Noun

• S: (n) pi (the ratio of the circumference to the diameter of a circle; approximately equal to 3.14159265358979323846...)
• S: (n) private detective, PI, private eye, private investigator, operative, shamus, sherlock (someone who can be employed as a detective to collect information)
• S: (n) principal investigator, PI (the scientist in charge of an experiment or research project)
• S: (n) pi (the 16th letter of the Greek alphabet)
• S: (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)