back door
1. Literally, an entrance located at the back of a building or place. When you get here, just come in the back door—I'll leave it unlocked for you.
2. Describing something that is done in a deceptive, corrupt, or indirect manner, especially with the intention of reducing the visibility of an action. The school board is trying to rush this major change through the back door, and we need to fight them on it!
back door
1. An entry at the rear of a building, as in Deliveries are supposed to be made at the back door only. [First half of 1500s]
2. A clandestine, unauthorized, or illegal way of operating. For example, Salesmen are constantly trying to push their products by offering special gifts through the back door . This term alludes to the fact that the back door cannot be seen from the front. [Late 1500s]