NOUN (2)

1. the hero of a romance by Cervantes; chivalrous but impractical;

2. any impractical idealist (after Cervantes' hero);

WordNet (r) 3.0 (2006):

Don Quixote
    n 1: the hero of a romance by Cervantes; chivalrous but
         impractical
    2: any impractical idealist (after Cervantes' hero)

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "Don Quixote":
   Bayard, Gawain, Lancelot, Quixote, Ritter, Sidney, Sir Galahad,
   bachelor, banneret, baronet, caballero, cavalier, chevalier,
   companion, daydreamer, dreamer, dreamer of dreams, enthusiast,
   escapist, idealist, knight, knight bachelor, knight banneret,
   knight baronet, knight-errant, lotus-eater, prophet, rhapsodist,
   romancer, romantic, romanticist, seer, utopian, utopianist,
   utopianizer, visionary, wishful thinker