castling vs fort

castling

noun
  • A miniature cast or mould. 

  • One that is cast. 

  • The act of constructing 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). 

  • A move in which the king moves two squares towards a rook, and the rook moves to the other side of the king; the action of the verb to castle. 

fort

noun
  • A structure improvised from furniture, bedding, etc., for playing games. 

  • Any permanent army post. 

  • An outlying trading-station, as in British North America. 

  • A fortified defensive structure stationed with troops. 

verb
  • To create a fort, fortifications, a strong point, or a redoubt. 

How often have the words castling and fort occurred in a corpus of books? (source: Google Ngram Viewer )