# pi

Pronunciation: say "PY" /paɪ/

## Noun

1. The irrational, transcendental constant equal to the ratio of a Euclidean circle's circumference to its diameter, approximately 3.14159 and usually written π.
   - Simple: A number, about 3.14, found by dividing the distance around a circle by the distance across it.
   - _The area of a circle equals pi times the square of its radius._
   - _Engineers often round pi to 3.1416 for quick calculations on site._
2. A Greek letter whose position is sixteenth in the Classical and Modern alphabets and seventeenth in Old Greek.
   - Simple: The 16th letter of the Greek alphabet. In an older Greek alphabet, it was the 17th.
   - _Above the fraternity house door hung a gold sigma and a gold pi._
   - _The stonemason misread the worn inscription, mistaking a pi for a gamma._

## Other meanings

- (noun) An abbreviation of pica, the typographic unit conventionally equal to 12 points, six of which make an inch.
- (noun) In letterpress printing, metal type that has been spilled, mixed together, or thrown into disorder.
- (verb) To spill or mix up printing type, throwing its letters out of order.
- (adjective) Of type or characters: outside a font's usual character set, especially non-Roman symbols rather than standard Roman letters and numerals.
- (noun) An abbreviation of piaster, a unit of currency.
- (adjective) Pious; showing earnest devotion to religion or to strict moral standards.

## Origin

From Ancient Greek πεῖ (peî), ultimately from Proto-Semitic *pay- ("mouth"); it is a doublet of pe. Its mathematical use apparently comes from its being the first letter of περιφέρεια (periphéreia, "periphery; circumference"), and was first recorded in 1706 in William Jones's Synopsis Palmariorum Matheseos.

Source: DictionaryAI, https://dictionaryai.com/define/pi (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).