A fortified residence, especially that of a prince or nobleman; a fortress.(noun)
source: webster1913
verb (v)
move the king two squares toward a rook and in the same move the rook to the square next past the king(verb.competition)
source: wordnet30
To move the castle to the square next to king, and then the king around the castle to the square next beyond it, for the purpose of covering the king.(verb)