doorstop

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A wedge inserted beneath a door to hold it open at a desired position.
• noun A weight or spring that prevents a door from slamming.
• noun A rubber-tipped projection attached to a wall to protect it from the impact of an opening door.

from The Century Dictionary.

• noun A strip of carriage-lace, or metal, used to prevent a carriage-door from opening beyond a fixed point.
• noun A flange against which a door shuts in its frame.
• noun A device placed behind a door to prevent it from being opened too widely.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Carp.) The block or strip of wood or similar material which stops, at the right place, the shutting of a door; any object used to stop open doors from moving.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any device or object used to halt the motion of a door, as a large or heavy object, a wedge, or some piece of hardware fixed to the floor, door or wall.
• noun humorous A large book, which by implication could be used to stop a door.
• noun UK (in error for doorstep) A thick sandwich.
• noun Australia An interview with a politician or other public figure (apparently informal or spontaneous but often planned), as they enter or leave a building.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a stop that keeps open doors from moving