Released from military service and returned to civilian life; the past tense of demob.
Past tense and past participle of 'demob' (demobilize). British military slang that became formalized. The '-ed' ending is standard past tense formation.
After WWII, millions of British soldiers used this casual word, and it became so common that it's now official—proving that even casual slang can become 'proper' English if enough important people use it!
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