jail: [13] Etymologically, a jail is a ‘little cage’. The word comes ultimately from Vulgar Latin *gaviola, which was an alteration of an earlier *caveola, a diminutive form of Latin cavea ‘cage’ (source of English cage). It passed into English in two distinct versions: jail came via Old French jaiole; but the Old Northern French form of the word was gaiole, and this produced English gaol.
Until the 17th century gaol was pronounced with a hard /g/ sound, but then it gradually fell into line phonetically with jail. There has been a tendency for British English to use the spelling gaol, while American prefers jail, but there are now signs that jail is on the increase in Britain. => cage[jail etymology, jail origin, 英语词源]