noun

1. a large building or group of buildings fortified with thick walls, battlements, and often a moat; castles were the strongholds of noblemen in the Middle Ages
2. any massive dwelling somewhat like this
3. a safe, secure place; refuge
4. Chess rook

Etymology: ME < OE & Anglo-Fr castel < L castellum, dim. of castrum, fort

transitive verb castled -·tled, castling -·tling

1. to put into, or furnish with, a castle
2. Chess to move (a king) two squares to either side and then, in the same move, set the castle in the square skipped by the king: permitted only when neither piece has been moved before and the spaces between them are not occupied

intransitive verb