noun

1. an upright structure of wood, stone, brick, etc., serving to enclose, divide, support, or protect; specif.,
   1. such a structure forming a side or inner partition of a building
   2. such a continuous structure serving to enclose an area, to separate fields, etc.
   3. such a structure used as a military defense; fortification
   4. such a structure used to hold back water; levee; dike
2. something resembling a wall in appearance or function, as the side or inside surface of a container or body cavity
3. something suggestive of a wall in that it holds back, divides, hides, etc. a wall of secrecy

Etymology: ME wal < OE weall (akin to Ger wall) < L vallum, rampart < vallus, a stake, palisade < IE base *wel-, to turn > walk

adjective

1. of or along a wall
2. placed or growing on, in, or against a wall

transitive verb

1. to furnish, line, enclose, divide, protect, etc. with or as with a wall or walls to wall a room with books, to wall off the old wing, a mind walled in by fears
2. to close up (an opening) with a wall: usually with up