gaiole

The word 'gaol' comes from Old Norman French gaiole (also gayole), meaning 'cage' or 'prison,' ultimately from Latin caveola, a diminutive of cavea, 'cage' or 'enclosure.' The word arrived in England with the Norman Conquest in 1066. But simultaneously, the Parisian French form jaiole (which became Modern French geole and English 'jail') also entered the language. England did not get one French word for prison; it got two, from two competing dialects.

The split persisted for centuries. English legal documents and official records used 'gaol' -- the Norman form favored by the courts and the government. Popular speech and informal writing used 'jail' -- the Parisian form that was easier to pronounce. Both referred to the same institution. The same prisoner in the same cell could be described as being in gaol in an official record and in jail in a letter home.

The divergence became a class marker. 'Gaol' was the spelling of judges, barristers, and civil servants. 'Jail' was the spelling of everyone else. British newspapers used 'gaol' well into the twentieth century; The Times of London did not officially switch to 'jail' until the 1980s. Australian English held onto 'gaol' even longer. American English chose 'jail' early and never looked back.

The pronunciation, regardless of spelling, has always been the same: /dʒeɪl/. The 'g' in 'gaol' is silent and has been for centuries. It is a fossil of Norman French orthography preserved in legal English long after spoken English abandoned it. The cage has one pronunciation and two spellings, a small monument to the fact that England was conquered by French speakers who could not agree on how to spell their own words.