castle in the air

Noun

castle in the air (plural castles in the air)

1. (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.
   • Many times ſuch men when they come to themſelves, tell ſtrange things of Heauen and Hell, what viſions they haue ſeene; […] The like effects almost are to bee ſeene in ſuch as are awake: How many Chimæras, Anticks, golden mountaines, and Caſtles in the Aire doe they build vnto themſelves?1624, Democritus Junior [pseudonym; Robert Burton], “Of the Force of Imagination”, in The Anatomy of Melancholy: […], 2nd edition, Oxford, Oxfordshire: […] John Lichfield and James Short, for Henry...
   • Look you, Amanda, you may build castles in the air, "and fume, and fret, and grow thin and lean, and pale and ugly, if you please." But I tell you, no man worth having is true to his wife, or can be true to his wife, or ever was, or will be so.1696, John Vanbrugh, The Relapse; or, Virtue in Danger. […] (Bell’s British Theatre; XXVI), London: Printed for the proprietors, under the Direction of John Bell, […], published 1795, →OCLC, act III...

   Synonyms:

   air castle, castles in Spain, castle in the skies, eggs in moonshine, jam tomorrow, pie in the sky, pipe dream

   Antonyms:

   terra firma, on solid ground