1. The ratio of the circumference to the diameter of a circle; approximately equal to 3.14159265358979323846 …
   "Students often memorize the first few digits of pi for maths competitions"
    
2. The 16th letter of the Greek alphabet
   "Pi is the symbol used to represent the ratio of a circle's circumference to its diameter"

1. The scientist in charge of an experiment or research project
   "As PI, she oversaw all aspects of the study";
   - principal investigator
    
2. An antiviral drug used against HIV; interrupts HIV replication by binding and blocking HIV protease; often used in combination with other drugs
   "The patient's HIV treatment regimen included a PI";
   - protease inhibitor
    
3. Someone who can be employed as a detective to collect information and assist in criminal investigations
   "The jealous husband hired a PI to follow his wife";
   - private detective, private eye, private investigator, operative, shamus, sherlock

Sounds like: phylum, um

Derived forms: PIs

Type of: alphabetic character, antiviral, antiviral agent, antiviral drug, detective, letter, letter of the alphabet, scientist, transcendental number

Part of: drug cocktail, Greek alphabet, HAART, highly active antiretroviral therapy

Encyclopedia: Pi, faith in chaos