CASTLE

I. noun Etymology: Middle English castel, from Old English, from Old French & Latin; Old French dialect (Norman-Picard) castel, from Latin castellum fortress, diminutive of castrum fortified place; perhaps akin to Latin castrare to castrate Date: before 12th century 1. a large fortified building or set of buildings, a massive or imposing house, a retreat safe against intrusion or invasion, rook III, II. verb (~d; castling) Date: 1587 transitive verb to establish in a ~, to move (the chess king) in castling, intransitive verb to move a chess king two squares toward a rook and in the same move the rook to the square next past the king