castle in the aircastle in the air
an imaginary scheme not likely to be realized; daydream
also castle in Spain
(plural castles in the air)
- (idiomatic) A visionary project or scheme; a day-dream; an idle fancy; a pipe dream; any plan, desire, or idea that is unlikely to be ever realized; a near impossibility.
- Completing the metaphor, one is said to build a castle in the air.