1911 Encyclopædia Britannica/Gaol

GAOL, or Jail, a prison (q.v.). The two forms of the word are due to the parallel dual forms in Old Central and Norman French respectively, jaiole or jaole, and gaiole or gayolle. The common origin is the med. Lat. gabiola, a diminutive formed from cavea, a hollow, a den, from which the English “cave” is derived. The form “gaol” still commonly survives in English, and is in official usage, e.g. “gaol-delivery,” but the common pronunciation of both words, “jail,” shows the real surviving word.