The Collaborative International Dictionary of English v.0.48:

Voluble \Vol"u*ble\, a. [L. volubilis, fr. volvere, volutum, to
   roll, to turn round; akin to Gr. ? to infold, to inwrap, ? to
   roll, G. welle a wave: cf. F. voluble. Cf. F. Well of
   water, Convolvulus, Devolve, Involve, Revolt, Vault
   an arch, Volume, Volute.]
   [1913 Webster]
   1. Easily rolling or turning; easily set in motion; apt to
      roll; rotating; as, voluble particles of matter.
      [1913 Webster]

   2. Moving with ease and smoothness in uttering words; of
      rapid speech; nimble in speaking; glib; as, a flippant,
      voluble, tongue.
      [1913 Webster]

            [Cassio,] a knave very voluble.       --Shak.
      [1913 Webster]

   Note: Voluble was used formerly to indicate readiness of
         speech merely, without any derogatory suggestion. "A
         grave and voluble eloquence." --Bp. Hacket.
         [1913 Webster]

   3. Changeable; unstable; fickle. [Obs.]
      [1913 Webster]

   4. (Bot.) Having the power or habit of turning or twining;
      as, the voluble stem of hop plants.
      [1913 Webster]

   Voluble stem (Bot.), a stem that climbs by winding, or
      twining, round another body.
      [1913 Webster] -- Vol"u*ble*ness, n. -- Vol"u*bly,
      adv.
      [1913 Webster]

WordNet (r) 3.0 (2006):

voluble
    adj 1: marked by a ready flow of speech; "she is an extremely
           voluble young woman who engages in soliloquies not
           conversations" [ant: taciturn]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "voluble":
   all jaw, bombastic, candid, chatty, communicative, conversational,
   effusive, expansive, exuberant, flip, fluent, frank, gabby,
   garrulous, gassy, glib, gossipy, gregarious, gushy, long-winded,
   loquacious, multiloquent, multiloquious, newsy, overtalkative,
   profuse, prolix, silver-tongued, smooth, sociable, talkative,
   talky, verbose, vocative, windy, wordy