CASTLE

Definition:

[noun] a large and stately mansion
Synonyms: palace
[noun] a large building formerly occupied by a ruler and fortified against attack
[noun] (chess) the piece that can move any number of unoccupied squares in a direction parallel to the sides of the chessboard
Synonyms: rook
[noun] interchanging the positions of the king and a rook
Synonyms: castling
[verb] move the king two squares toward a rook and in the same move the rook to the square next past the king