1.a swinging or sliding barrier that will close the entrance to a room or building or vehicle;
he knocked on the door
2.the entrance (the space in a wall) through which you enter or leave a room or building; the space that a door can close;
he stuck his head in the doorway
3.anything providing a means of access (or escape);
we closed the door to Haitian immigrants
4.a structure where people live or work (usually ordered along a street or road);
the office next door
5.a room that is entered via a door;
his office is the third door down the hall on the left