Etymology

perfidious

per·fid·i·ous
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Today it means: Of, pertaining to, or representing perfidy; disloyal to what should command one's fidelity or allegiance. Full definition →

First used late 16th c.Latin perfidiōsus ← Proto-Indo-European *h₃édosder.? ← Proto-Italic *per
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The story

  1. Proto-Indo-European*per-der.?
  2. Proto-Indo-European*pér
  3. Proto-Italic*per
  4. Latinper
  5. Proto-Indo-European*bʰeydʰ-
  6. Latinfidēs
  7. Latinperfidus
  8. Latinperfidia
  9. Proto-Indo-European*h₃ed-
  10. Proto-Indo-European*h₃édosder.?
  11. Latinperfidiōsus
  12. English todayperfidious

From Latin perfidiōsus (“treacherous”), from perfidia. By surface analysis, perfidy + -ous.

First known use, by meaning

  • from late 16th c. Of, pertaining to, or representing perfidy; disloyal to what should command one's fidelity or allegiance.

Etymology from Wiktionary, CC BY-SA 4.0.