(construction) A double wall of masonry connected by an air space.

(idiomatic) alternative form of writing on the wall

(physics) An interface separating magnetic domains. / (astrophysics) A two-dimensional singularity hypothesized in string theory.

plural of cell wall

(history) A wall that parted the city of Berlin until 1989, constructed by the German Democratic Republic to keep East Germans from escaping to West Berlin.

(politics) Any barrier designed to keep people from crossing a border, e.g. the one proposed to keep people from crossing from Mexico into the United States.

plural of Chinese Wall

Short for Great Wall of China. / (astronomy) Either of two identified areas containing hundreds of galaxies.

(transitive) To seal with a wall.

To separate with a wall. / (figuratively, by extension) To isolate completely.