A large residential building or compound that is fortified and contains many defences; in previous ages often inhabited by a nobleman or king. Also, a house or mansion with some of the architectural features of medieval castles.
An instance of castling.
(informal) A rook; a chess piece shaped like a castle tower.
A defense structure in shogi formed by defensive pieces surrounding the king.
(obsolete) A close helmet.
Any strong, imposing, and stately palace or mansion.
A small tower, as on a ship, or an elephant's back.
(colloquial) The wicket.

To house or keep in a castle.
To protect or separate in a similar way.
(obsolete) To make into a castle: to build in the form of a castle or add (real or imitation) battlements to an existing building.
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.
To create a similar defensive position in Japanese chess through several moves.
To bowl a batsman with a full-length ball or yorker such that the stumps are knocked over.