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). [ORIGIN: from the initial letter of Greek periphereia ‘circumference.’ ]
• ( Pi) [followed by Latin genitive] Astronomy the sixteenth star in a constellation : Pi Herculis.
• Chemistry & Physics relating to or denoting an electron or orbital with one unit of angular momentum about an internuclear axis.