pi

Meanings

1. 1
   noun

   The number (about 3.14159) you get when you divide a circle's circumference by its diameter.

   To find the area of a circle, multiply pi by the radius squared.

2. 2
   noun

   The sixteenth letter of the Greek alphabet (Π, π).

   The Greek letter pi is written as a small loop with two legs.

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.

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