back doornoun
[ C ] a door at the back or side of a building, or at the back of a vehicle:
There's someone at the back door.
He opened the back door and gestured for her to get into the car.
[ S ] used to refer to an indirect way of achieving something, especially so that people do not know about it and so cannot object to it:
HMI is to be privatised by the back door because the half of HMI who will not be employed by it will have to go and set up as private consultants.
The data collection exercise was designed to open the back door to an energy consumption tax on home owners.