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. castles in the air (or in Spain) a visionary unattainable scheme; a day-dream. castled adj.
[ AF & ONF castel, chastel f. L castellum dimin. of castrum fort ]