wall 
(wôl)
(wôl)n.
1. An upright structure of masonry, wood, plaster, or other building material serving to enclose, divide, or protect an area, especially a vertical construction forming an inner partition or exterior siding of a building.
2. often walls A continuous structure of masonry or other material forming a rampart and built for defensive purposes.
3. A structure of stonework, concrete, or other material built to retain a flow of water.
4.
a. Something resembling a wall in appearance, function, or construction, as the exterior surface of a body organ or part: the abdominal wall.
b. Something resembling a wall in impenetrability or strength: a wall of silence; a wall of fog.
c. An extreme or desperate condition or position, such as defeat or ruin: driven to the wall by poverty.
5. Sports The vertical surface of an ocean wave in surfing.
tr.v. walled, wall·ing, walls
Idioms: 1. To enclose, surround, or fortify with or as if with a wall: wall up an old window. See Synonyms at enclose.
2. To divide or separate with or as if with a wall. Often used with off: wall off half a room.
3. To confine or seal behind a wall; immure: "I determined to wall [the body] up in the cellar" (Edgar Allan Poe).
4. To block or close (an opening or passage, for example) with or as if with a wall.
off the wall Slang
1. Extremely unconventional.
2. Without foundation; ridiculous: an accusation that is really off the wall.
up the wall Slang
Into a state of extreme frustration, anger, or distress: tensions that are driving me up the wall.
writing/handwriting on the wall
An ominous indication of the course of future events: saw the writing on the wall and fled the country.
[Middle English, from Old English weall, from Latin vallum, palisade, from vallus, stake. Idiom, in reference to an incident in the Bible (Daniel 5) in which a hand writes mysterious words on the wall of Belshazzar's banquet hall and the prophet Daniel interprets them as predicting the king's downfall.]
wallless adj.