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From Ancient Greek ??? (peî). Its mathematical use apparently stems from its use as the first letter in ?????????? (periféreia, “periphery; circumference”) and was first cited in 1706 in the Synopsis Palmariorum Matheseos by William Jones.
pi (countable and uncountable, plural pis)
- The 16th letter of the Classical and Modern Greek alphabets and the seventeenth in Old Greek.
- (mathematics) An irrational and transcendental constant representing the ratio of the circumference of a Euclidean circle to its diameter; approximately 3.14159265358979323846264338327950; usually written ?.
- (letterpress typography) Metal type that has been spilled, mixed together, or disordered. Also called pie.
pi (not comparable)