Etymology

femtosecond

F4E1M3T1O1S1E1C3O1N1D2

Today it means: An SI unit of time equal to 10⁻¹⁵ seconds. Symbol: fs Full definition →

English second ← Middle English secunde ← Old French seconde
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The story

  1. Proto-Indo-European*pénkʷe
  2. Proto-Germanic*fimf
  3. Proto-Indo-European*déḱm̥
  4. Proto-Germanic*tehun
  5. Proto-Germanic*fimftehun
  6. Old Norsefimmtán
  7. Danishfemten
  8. Englishfemto-
  9. Old Frenchseconde
  10. Middle Englishsecunde
  11. Englishsecond
  12. English todayfemtosecond

From femto- + second.

Etymology from Wiktionary, CC BY-SA 4.0.