The Collaborative International Dictionary of English v.0.48:

Prolix \Pro*lix"\ (?; 277), a. [L. prolixus extended, long,
   prolix, probably fr. pro before, forward + liqui to flow,
   akin to liquidus liquid; cf. OL. lixa water: cf. F. prolixe.
   See Liquid.]
   [1913 Webster]
   1. Extending to a great length; unnecessarily long; minute in
      narration or argument; excessively particular in detail;
      -- rarely used except with reference to discourse written
      or spoken; as, a prolix oration; a prolix poem; a prolix
      sermon.
      [1913 Webster]

            With wig prolix, down flowing to his waist.
                                                  --Cowper.
      [1913 Webster]

   2. Indulging in protracted discourse; tedious; wearisome; --
      applied to a speaker or writer.
      [1913 Webster]

   Syn: Long; diffuse; prolonged; protracted; tedious; tiresome;
        wearisome.

   Usage: Prolix, Diffuse. A prolix writer delights in
          circumlocution, extended detail, and trifling
          particulars. A diffuse writer is fond of amplifying,
          and abounds in epithets, figures, and illustrations.
          Diffuseness often arises from an exuberance of
          imagination; prolixity is generally connected with a
          want of it.
          [1913 Webster]

WordNet (r) 3.0 (2006):

prolix
    adj 1: tediously prolonged or tending to speak or write at great
           length; "editing a prolix manuscript"; "a prolix lecturer
           telling you more than you want to know" [ant: concise]