From Ancient Greek πεῖ (peî). Its mathematical use apparently stems from its use as the first letter in περιφέρεια (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 π.
- (letterpress typography) Metal type that has been spilled, mixed together, or disordered. Also called pie.
pi (third-person singular simple present pies, present participle piing, simple past and past participle pied)
- (letterpress typography) To spill or mix printing type. Also, "to pie".
pi (not comparable)
- (typography) Not part of the usual font character set; especially, non-Roman type or symbols as opposed to standard alphanumeric Roman type.