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]

Moby Thesaurus II by Grady Ward, 1.0:

89 Moby Thesaurus words for "prolix":
   all jaw, blah, broken-record, candid, chatty, communicative,
   conversational, de longue haleine, de trop, diffuse, dispensable,
   drearisome, dreary, dry, dryasdust, dull, dusty, effusive, endless,
   everlasting, excess, expansive, expendable, expletive, extended,
   filled out, flip, fluent, frank, gabby, garrulous, gassy, glib,
   gossipy, gratuitous, gregarious, gushy, harping, humdrum,
   in excess, invariable, irksome, jog-trot, lengthy, long,
   long-drawn-out, long-spun, long-winded, longiloquent, loquacious,
   monotonous, multiloquent, multiloquious, needless, newsy,
   nonessential, overtalkative, padded, pleonastic, prolonged,
   protracted, redundant, singsong, smooth, sociable, spare, spun-out,
   supererogatory, superfluous, talkative, talky, tautologic,
   tautologous, tedious, tiresome, to spare, treadmill, uncalled-for,
   unessential, uneventful, unnecessary, unneeded, unrelenting,
   unvarying, verbose, voluble, wearisome, windy, wordy