(idiomatic) Wildly unconventional; bizarre; absurd. / (idiomatic) Of a person's behaviour: greatly inappropriate.

Alternative spelling of off-the-wall

(US, idiomatic, slang) With maximum effort or commitment.

(idiomatic) An ominous warning; a prediction of bad luck.

A restaurant, shop or other establishment catering to customers that is particularly inconspicuous and easily overlooked. / (colloquial, chiefly Britain) An automated teller machine (ATM).

(idiomatic) A very difficult situation with no beneficial options available for action.

a hand railing attached to a wall

(idiomatic) A quiet, non-participating, or unseen observer; an eavesdropper or witness.

(cytology) A thick, fairly rigid, layer formed around individual cells of bacteria, Archaea, fungi, plants, and algae (but not animals and other protists which generally have cell membranes without cell walls). The cell wall is external to the cell membrane and serves a structural function helping the cell maintain its shape and protecting the cell from damage.

(performing arts, idiomatic) The imaginary invisible wall at the front of the stage in a proscenium theatre, through which the audience sees the action in the world of the play.