castle

Noun

• interchanging the positions of the king and a rook

• (chess) the piece that can move any number of unoccupied squares in a direction parallel to the sides of the chessboard

• a large building formerly occupied by a ruler and fortified against attack

• a large and stately mansion

Verb

• move the king two squares toward a rook and in the same move the rook to the square next past the king

Related words

• Synonyms: 
  castling , rook , palace