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pi

Etymology and origin of the English word pi

History Permalink
Confidence
Established
Formation
Borrowing
First attested
15th century
Ultimate origin
Ancient Greek (πῖ)

Pronunciation

Etymology

It is the name of the Greek letter Ancient Greek πῖ (pî),[2][3] which is of Semitic origin.[2] Etymonline says it came from Phoenician, literally “little mouth”.[4] As the mathematical constant, π stands for περιφέρεια (periphéreia, “periphery”) (see periphery).[5][4][6][7]

Earliest recorded meaning

The name of the letter: the 15th century in Merriam-Webster.[2]

Semantic evolution

The Swiss mathematician Leonhard Euler used π for the ratio of a circle's circumference to its diameter in Latin in 1748,[4][5][3] and the use is found in English from 1841.[5][4] In electrical engineering a pi network is from 1924, and in physics and chemistry pi electrons and bonds from 1929.[3]

Timeline

  • 15th century – the letter pi.[2]
  • 1748 – π for the circle ratio (Euler, in Latin).[4][3]
  • 1841 – pi (mathematics, English).[5][4]
  • 1929 – pi electrons.[3]

Modern meaning

Noun

  1. The 16th letter of the Greek alphabet (Π, π).
  2. (mathematics) The ratio of the circumference of a circle to its diameter, a transcendental number of about 3.14159.

Word family

  • pion
  • pi meson

Usage notes

Pi, jumbled printing type, is a variant of pie.[4][3][8] An old school slang pi, pious or sanctimonious, is from about 1870.[3]

References

  1. ^ Jones, Daniel (2011), Cambridge English Pronouncing Dictionary, 18th ed., ed. Peter Roach, Jane Setter and John Esling, Cambridge: Cambridge University Press
  2. ^ a b c d Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
  3. ^ a b c d e f g Simpson, J. A.; Weiner, E. S. C., eds. (1989), The Oxford English Dictionary, 2nd ed., Oxford: Clarendon Press
  4. ^ a b c d e f g Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  5. ^ a b c d Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
  6. ^ Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
  7. ^ Collins English Dictionary (2023), Glasgow: HarperCollins
  8. ^ The American Heritage Dictionary of the English Language (1992), 3rd ed., Boston: Houghton Mifflin
Cite this entry

“Pi.” Etymologically, 17 Oct. 2026, etymologically.com/en/pi. Accessed 17 Oct. 2026.

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