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1. A large and stately mansion
   - palace
    
2. A large building formerly occupied by a ruler and fortified against attack
    
3. (chess) the piece that can move any number of unoccupied squares in a direction parallel to the sides of the chessboard
   - rook
    
4. Interchanging the positions of the king and a rook
   - castling

1. Move the king two squares toward a rook and in the same move the rook to the square next past the king

Derived forms: castling, castles, castled

Type of: chess move, chess piece, chessman, fortification, go, hall, manse [archaic], mansion, mansion house, move, munition, residence

Encyclopedia: Castle, New Rochelle Castle, Bedford Castle Castle, Newcastle upon Tyne Castle, Swansea Castle, Oklahoma Castle, OK