castle

ot noun

1. A large building that is fortified and contains many defences; in previous ages often inhabited by a nobleman or king.
2. An instance of castling.
3. A rook; a chess piece shaped like a castle tower.
4. A defense structure in shogi formed by defensive pieces surrounding the king.

fe’l verb

1. To house or keep in a castle.
2. To protect or separate in a similar way.
3. To make into a castle: to build in the form of a castle or add (real or imitation) battlements to an existing building.
4. (usually intransitive) To move the king 2 squares right or left and, in the same turn, the nearest rook to the far side of the king. The move now has special rules: the king cannot be in, go through, or end in check; the squares between the king and rook must be vacant; and neither piece may have been moved before castling.