pi
Pluralpis
Pluralpis
- 1The irrational, transcendental constant equal to the ratio of a Euclidean circle's circumference to its diameter, approximately 3.14159 and usually written π.
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.
Note
Mathematicians borrowed the Greek letter probably because it begins periphéreia, the Greek word for circumference; William Jones is the first on record to use it so, in his Synopsis Palmariorum Matheseos of 1706. Transcendental says more than irrational: pi is the root of no nonzero polynomial equation with whole-number coefficients.
Checked 1 Nov 2026 · 6 facts
- The mathematical symbol probably derives from the initial letter of the Greek word for periphery or circumference. en.wikipedia.org
- Greek periphéreia means circumference. en.wiktionary.org
- William Jones first used π alone for the circumference-to-diameter ratio in 1706. en.wikipedia.org
- Jones's Synopsis Palmariorum Matheseos was published in 1706. e-rara.ch
- Transcendence is a stronger property than irrationality for real numbers. kconrad.math.uconn.edu
- The zero polynomial must be excluded: every number satisfies it. The precise statement is that pi is not a root of any nonzero polynomial with integer coefficients. en.wikipedia.org
- 2A Greek letter whose position is sixteenth in the Classical and Modern alphabets and seventeenth in Old Greek.
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.
Note
The name runs back through Ancient Greek to a Semitic word for "mouth", and English has it twice, since pe is the same name arriving by another route. Lowercase, as π, it also stands for the circle constant.
Checked 2 Nov 2026 · 2 facts
- The name pi comes through Ancient Greek ultimately from a Semitic word meaning mouth. en.wiktionary.org
- English pi and pe are doublets, inherited through different borrowing routes. en.wiktionary.org
- 3An abbreviation of pica, the typographic unit conventionally equal to 12 points, six of which make an inch.
- 4In letterpress printing, metal type that has been spilled, mixed together, or thrown into disorder.
- 5To spill or mix up printing type, throwing its letters out of order.
- 6Of type or characters: outside a font's usual character set, especially non-Roman symbols rather than standard Roman letters and numerals.
- 7An abbreviation of piaster, a unit of currency.
- 8Pious; showing earnest devotion to religion or to strict moral standards.
“Those are very 'pi' sentiments. Was a preacher in Staffordshire— I was raised chapel, though've tried to forget it—he talked that way... redemption and the lot.”
1972, Anya Seton, Green Darkness
Showing meanings only.
Practice
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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.
Checked 1 Nov 2026 · 5 facts
- Pi derives from Ancient Greek πεῖ, ultimately from Proto-Semitic *pay-, meaning mouth. en.wiktionary.org
- Pi and pe are doublets. en.wiktionary.org
- The mathematical symbol apparently derives from the initial letter of περιφέρεια. en.wikipedia.org
- Ancient Greek περιφέρεια means periphery or circumference. en.wiktionary.org
- The first recorded use of π alone for the circumference-to-diameter ratio was in William Jones's Synopsis Palmariorum Matheseos in 1706. en.wikipedia.org