pi

pi¹ [pʌɪ]

noun

1》 the sixteenth letter of the Greek alphabet (Π, π), transliterated as ‘p’.

2》 the numerical value of the ratio of the circumference of a circle to its diameter (approximately 3.14159).

3》 [as modifier] Chemistry & Physics (of an electron or orbital) with one unit of angular momentum about an internuclear axis.

symbol (Π) mathematical product.

Origin

from Gk: the numerical use comes from the initial letter of Gk periphereia 'circumference'.

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pi² [pʌɪ]

adjective Brit. informal short for pious.