BACK DOOR Meaning of BACK DOOR in English ■ noun1》 the rear door of a building. 2》 [as modifier ] underhand; clandestine: a back-door tax increase. Phrasesby (or through ) the ~ in a clandestine or underhand way. Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004