castle in the air

American  

noun

1. a fanciful or impractical notion or hope; daydream.

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castle in the air British  

noun

1. a hope or desire unlikely to be realized; daydream

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Etymology

Origin of castle in the air

First recorded in 1570–80

Example Sentences

“Before you started building castles in the air,” Josie said loyally.

From Literature

All entrepreneurs making pitches to venture capital funds are inclined to promise castles in the air and riches beyond the dreams of Croesus, or they won’t be invited through the door.

From Los Angeles Times

“Wouldn’t it be fun if all the castles in the air which we make could come true, and we could live in them?” said Jo, after a little pause.

From Literature

"At a time when the pandemic is killing thousands, crematoria are full and graveyards have run out of space, the government is building castles in the air."

From BBC

In the Scientific Revolution, Bacon and Descartes were amongst those with plans for thoroughgoing intellectual change, but their plans were castles in the air, and neither of them imagined what Newton would achieve.

From Literature