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Definition pi


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 (plural pis)

  1. The 16th letter of the Classical and Modern Greek alphabets and the seventeenth in Old Greek.
  2. (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.
  3. (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)

  1. (letterpress typography) To spill or mix printing type. Also, "to pie".


pi (not comparable)

  1. (typography) Not part of the usual font character set; especially, non-Roman type or symbols as opposed to standard alphanumeric Roman type.

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