n. & v.
--n.
1. a a large fortified building or group of buildings; a stronghold. b a formerly fortified mansion.
2 Chess ROOK(2).
--v. Chess 1 intr. make a special move (once only in a game on each side) in which the king is moved two squares along the back rank and the nearer rook is moved to the square passed over by the king.
2 tr. move (the king) by castling.
Phrases and idioms:
castles in the air (or in Spain) a visionary unattainable scheme; a day-dream.
Derivatives:
castled adj.
Etymology: AF & ONF castel, chastel f. L castellum dimin. of castrum fort