Definition: interchanging the positions of the king and a rook
Main entry: castle
Definition: a large building formerly occupied by a ruler and fortified against attack
Definition: (chess) the piece that can move any number of unoccupied squares in a direction parallel to the sides of the chessboard
Definition: a large and stately mansion
Main entry: castle
Definition: move the king two squares toward a rook and in the same move the rook to the square next past the king