plural of castle in the air

(idiomatic) A desire, idea, or plan that is unlikely to ever be realized; a visionary project or scheme; a daydream, an idle fancy, a near impossibility.

(idiomatic) From nowhere or nothing; from a non-existent or unknown source.

Free of moisture to the degree possible by exposure to air (moisture contents of the object and air are in equilibrium); "naturally" dried.

To dry by exposure to the air.

A person whose responsibility was to defend a particular building during an air raid, ensure the blackout was complete, and assist civilians to an air-raid shelter.

a jet engine where a gas generator drives the turbine that drives the inlet compressor

plural of first-aid box

Leave something alone; avoid attempting to correct, fix, or improve what is already sufficient (often with an implication that the attempted improvement is risky and might backfire).

plural of air pump