pi

/paɪ/

pi

English Noun Top 10,478

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Definition

The sixteenth letter of the Classical and Modern Greek alphabets and the seventeenth in Old Greek.

Etymology

From Koine Greek πῖ (pî), from Ancient Greek πεῖ (peî), ultimately from Proto-Semitic *pay- (“mouth”). Doublet of pe. Its mathematical use apparently stems from its use as the first letter in περιφέρεια (periphéreia, “periphery; circumference”) and was first cited in 1706 in the Synopsis Palmariorum Matheseos by William Jones.