Etymology

factorial

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Today it means: The result of multiplying a given number of consecutive integers from 1 to the given number. In equations, it is symbolized by an exclamation mark (!). For example, 5! = 1 × 2 × 3 × 4 × 5 = 120. Full definition →

Proto-Indo-European *h₂élisder.? ← English factor ← Middle English factour
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The story

  1. Proto-Indo-European*dʰeh₁-
  2. Proto-Indo-European*dʰeh₁k-
  3. Proto-Indo-European*dʰh₁kyéti
  4. Proto-Italic*θakjō
  5. Proto-Italic*fakjō
  6. Latinfaciō
  7. Latinfactor
  8. Middle Frenchfacteur
  9. Latinfactor
  10. Anglo-Normanfactour
  11. Middle Englishfactour
  12. Englishfactor
  13. Proto-Indo-European*h₂el-
  14. Proto-Indo-European*h₂élisder.?
  15. English todayfactorial

From factor + -ial.

Etymology from Wiktionary, CC BY-SA 4.0.