[cas.tle] n [ME castel, fr. OE, fr. ONF, fr. L castellum fortress, castle, dim. of castrum fortified place; perh. akin to L castrare to castrate] (bef. 12c) 1 a: a large fortified building or set of buildings b: a massive or imposing house
2: a retreat safe against intrusion or invasion
3: [3]rook
[2]castle vb cas.tled ; cas.tling vt (1587) 1: to establish in a castle
2: to move (the chess king) in castling ~ vi: to move a chess king two squares toward a rook and in the same move the rook to the square next past the king