redoubt: [17] Redoubt ‘stronghold’ has no etymological connection with doubt (although redoubtable [14] does – it derives from the French ancestor of doubt, which originally meant ‘fear’, and so historically denotes ‘to be feared’). It was borrowed from French redoute, which goes back via obsolete Italian ridotta to medieval Latin reductus ‘hidden place, refuge’, a noun use of the past participle of Latin redūcere ‘bring back, withdraw’ (source of English reduce). The b was inserted under the influence of redoubtable. => reduce[redoubt etymology, redoubt origin, 英语词源]