Source : Webster's Revised Unabridged Dictionary (1913)

Idealism \I*de"al*ism\, n.
   The practice or habit of giving or attributing ideal form or
   character to things; treatment of things in art or literature
   according to ideal standards or patterns; -- opposed to
   {realism}.

Idealism \I*de"al*ism\, n. [Cf. F. id['e]alisme.]
   1. The quality or state of being ideal.

   2. Conception of the ideal; imagery.

   3. (Philos.) The system or theory that denies the existence
      of material bodies, and teaches that we have no rational
      grounds to believe in the reality of anything but ideas
      and their relations.

Source : WordNet®

idealism
     n 1: (philosophy) the philosophical theory that ideas are the
          only reality
     2: impracticality by virtue of thinking of things in their
        ideal form rather than as they really are
     3: elevated ideals or conduct; the quality of believing that
        ideals should be pursued [syn: {high-mindedness}, {noble-mindedness}]