the sixteenth letter of the Greek alphabet (Π, π), transliterated as ‘p’.
the numerical value of the ratio of the circumference of a circle to its diameter (approximately 3.14159).
[from the initial letter of Greek periphereia 'circumference']
(Pi) [followed by Latin genitive] Astronomy the sixteenth star in a constellation:Pi Herculis
[as modifier] Chemistry & Physics relating to or denoting an electron or orbital with one unit of angular momentum about an internuclear axis:the π orbital system of the benzene molecule
