1. A European bird, Corvus frugilegus, that belongs to the crow family: During their trip around Europe, Jack and Jill noticed many rooks that nested in treetop colonies.
2. A person who swindles or cheats: In the story, the crock turned out to be a real rook who tricked people into giving him a lot of money.
3. One of the black or white chessboard pieces; a castle: Tom explained that a rook could be moved either in a straight line forward or in a straight line sideways on the chess board during a game.