A Castle

A large building that is fortified and contains many defences; in previous ages often inhabited by a nobleman or king.
(chess) An instance of castling.
(chess, informal) A rook; a chess piece shaped like a castle tower.
(shogi) A defense structure in Japanese chess in which the king (玉) is positioned in a certain way so that it is protected by pawns (歩) and silver general(s) (銀) and/or gold general(s) (金) often with an additional knight (桂) and lance (香車).
(obsolete) A close helmet.
(dated) Any strong, imposing, and stately mansion.
(dated) A small tower, as on a ship, or an elephant's back.

For the chess piece, chess players prefer the term rook.