means The upright structures that enclose a room or building, dividing inside from outside and one space from another.

from From Old English 'weall,' meaning a rampart or earthwork — and here's the twist: the Anglo-Saxons borrowed it straight from Latin 'vallum,' the fortified palisade Roman soldiers threw up around their camps. So every bedroom wall carries a faint memory of a legionary's stockade, built to keep the barbarians (and, evidently, your neighbors' opinions) at bay.