Etymology

foolproof

F4O1O1L1P3R1O1O1F4

Today it means: Of a device: protected against, or designed to be proof against, misuse or error. Full definition →

English proof ← Middle English fol ← Old French fo
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The story

  1. Proto-Indo-European*bʰelǵʰ-
  2. Latinfollis
  3. Old Frenchfo
  4. Middle Englishfol
  5. Englishfool
  6. Englishproof
  7. English todayfoolproof

From fool + -proof.

Etymology from Wiktionary, CC BY-SA 4.0.