Etymologically
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phi

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Pronunciation

  • /faɪ/, /fiː/[1]

Etymology

The OED takes it as borrowed from Late Latin phi, recorded from the late 4th century,[2] from Ancient Greek φεῖ (pheî), the Greek name of the letter Φ, φ.[2][3] The American Heritage Dictionary gives the later form φῖ (phî) as the immediate source,[4] and Merriam-Webster derives the word from Middle Greek.[5]

Earliest recorded meaning

The name of the twenty-first letter of the Greek alphabet: perhaps before 1425, in Mandeville's Travels.[2][6] Merriam-Webster also dates it to the 15th century.[5]

Semantic evolution

The letter was originally an aspirated p, as in upheave, and later came to be pronounced f;[3] the Romans wrote it ph, which is why English spells Greek words that way.[7][3] As a Greek numeral, φ with a stroke stood for 500.[3] The Shorter Oxford notes that the English word was rare before the mid 19th century.[6] In the 20th century the letter became the name of technical quantities: a measure of the size of sediment particles in geology (1934),[2][6] the phi coefficient in statistics,[6] and the phi meson in particle physics (1962).[2][6] In mathematics φ often denotes a plane angle or a polar coordinate.[8]

Timeline

  • c. 1425 – the name of the Greek letter Φ, φ, in Mandeville's Travels.[2][5]
  • 1934 – in geology, an index of particle size.[2][6]
  • 1962 – in particle physics, the phi meson.[2][6]

Meanings

Noun

  1. The twenty-first letter of the Greek alphabet (Φ, φ), transliterated as ph or f.[9][5][4][2]
  2. (geology) An index of the size of sediment particles, the negative logarithm to base 2 of the diameter in millimetres.[2][6]
  3. (particle physics) A meson of a group with the same quantum numbers as the omega meson; in full, phi meson.[2][6]
  4. (statistics) In phi coefficient, a measure of correlation between two variables that can each take only two values.[6]

Word family

  • phi phenomenon
  • ph

References

  1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
  2. ^ a b c d e f g h i j k Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
  3. ^ a b c d The Chambers Dictionary (2014), 13th ed., Edinburgh: Chambers
  4. ^ a b The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
  5. ^ a b c d Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
  6. ^ a b c d e f g h i j Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
  7. ^ Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  8. ^ Soanes, Catherine; Stevenson, Angus, eds. (2004), Concise Oxford English Dictionary, 11th ed., Oxford: Oxford University Press
  9. ^ Collins English Dictionary (2023), Glasgow: HarperCollins