The crossword solution for the term 'QUIXOTE ADVERSARY' is 'WINDMILL'. Don Quixote, a novel by Spanish author Miguel de Cervantes, tells the story of an elderly man who believes himself to be a knight errant and sets out on a quest to revive chivalry. One of the most iconic scenes in the novel is when Don Quixote mistakes a windmill for a giant and charges at it with his lance. This scene serves as a metaphor for Don Quixote's misguided idealism and his tendency to see the world through rose-colored glasses. The windmill thus serves as an adversary to Don Quixote's delusions.