"castle" in the noun sense
1. palace, castle
a large and stately mansion
a large building formerly occupied by a ruler and fortified against attack
3. castle, rook
chess) the piece that can move any number of unoccupied squares in a direction parallel to the sides of the chessboard
4. castle, castling
interchanging the positions of the king and a rook
"castle" in the verb sense
move the king two squares toward a rook and in the same move the rook to the square next past the king
Source: WordNet® (An amazing lexical database of English)
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