The Collaborative International Dictionary of English v.0.48:

Reverie \Rev"er*ie\, Revery \Rev"er*y\, n.; pl. Reveries. [F.
   r['e]verie, fr. r[^e]ver to dream, rave, be light-headed. Cf.
   Rave.]
   1. A loose or irregular train of thought occurring in musing
      or mediation; deep musing; daydream. "Rapt in nameless
      reveries." --Tennyson.
      [1913 Webster]

            When ideas float in our mind without any reflection
            or regard of the understanding, it is that which the
            French call revery, our language has scarce a name
            for it.                               --Locke.
      [1913 Webster]

   2. An extravagant conceit of the fancy; a vision. [R.]
      [1913 Webster]

            There are infinite reveries and numberless
            extravagancies pass through both [wise and foolish
            minds].                               --Addison.
      [1913 Webster]

WordNet (r) 3.0 (2006):

reverie
    n 1: absentminded dreaming while awake [syn: reverie,
         revery, daydream, daydreaming, oneirism, air
         castle, castle in the air, castle in Spain]
    2: an abstracted state of absorption [syn: reverie, revery]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "reverie":
   Walter Mitty, absence of mind, absentmindedness, absorption,
   abstractedness, abstraction, amnesia, bad dream, bemusement,
   brown study, castle-building, catalepsy, cataplexy,
   catatonic stupor, close study, concentration, contemplation,
   contemplativeness, daydream, daydreamer, daydreaming, daze,
   deep thought, depth of thought, dream, dream state, dreaming,
   engrossment, fantasy, fantasying, fit of abstraction, fugue,
   fugue state, hypnotic trance, incubus, meditation, melancholy,
   mooning, moonraking, muse, musefulness, musing, muted ecstasy,
   nightmare, pensiveness, pipe dream, pipe-dreaming, preoccupation,
   profound thought, reflectiveness, sleepwalking, somnambulism,
   speculativeness, stargazing, study, stupor, thought,
   thoughtfulness, trance, vision, wistfulness, woolgathering