Cas·tle n.
 1. A fortified residence, especially that of a prince or nobleman; a fortress.
    The house of every one is to him castle and fortress, as well for his defense againts injury and violence, as for his repose.   --Coke.
 Our castle's strength
 Will laugh a siege to scorn.   --Shak.
 Note: ☞ Originally the mediæval castle was a single strong tower or keep, with a palisaded inclosure around it and inferior buidings, such as stables and the like, and surrounded by a moat; then such a keep or donjon, with courtyards or baileys and accessory buildings of greater elaboration a great hall and a chapel, all surrounded by defensive walls and a moat, with a drawbridge, etc. Afterwards the name was retained by large dwellings that had formerly been fortresses, or by those which replaced ancient fortresses.
 2. Any strong, imposing, and stately mansion.
 3. A small tower, as on a ship, or an elephant's back.
 4. A piece, made to represent a castle, used in the game of chess; a rook.
 Castle in the air, a visionary project; a baseless scheme; an air castle; -- sometimes called a castle in Spain (F. Château en Espagne).
 Syn: -- Fortress; fortification; citadel; stronghold. See Fortress.
 castle in the air
      n : absent-minded dreaming while awake [syn: reverie, revery,
           daydream, daydreaming, oneirism, air castle, castle
          in Spain]