The Collaborative International Dictionary of English v.0.48:

Idealist \I*de"al*ist\, n. [Cf. F. id['e]aliste.]
   1. One who idealizes; one who forms picturesque fancies; one
      given to romantic expectations.
      [1913 Webster]

   2. One who holds the doctrine of idealism, in any sense. In
      senses 4 and 5 of idealism, opposed to realist.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

idealist
    n 1: someone guided more by ideals than by practical
         considerations [syn: idealist, dreamer]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "idealist":
   Berkeleian, Don Quixote, Hegelian, Kantian, Neoplatonic,
   Neoplatonist, Neoplatonistic, Platonic, Platonist, Platonistic,
   Quixote, animist, animistic, daydreamer, dreamer,
   dreamer of dreams, enthusiast, escapist, idealistic, immaterialist,
   lotus-eater, panpsychist, panpsychistic, prophet, psychist,
   rhapsodist, romancer, romantic, romanticist, seer, solipsistic,
   spiritualist, spiritualistic, unrealistic, utopian, utopianist,
   utopianizer, visionary, wishful thinker