Source : Webster's Revised Unabridged Dictionary (1913)

Taciturn \Tac"i*turn\, a. [L. taciturnus: cf. F. taciturne. See
   {Tacit}.]
   Habitually silent; not given to converse; not apt to talk or
   speak. -- {Tac"i*turn*ly}, adv.

   Syn: Silent; reserved.

   Usage: {Taciturn}, {Silent}. Silent has reference to the act;
          taciturn, to the habit. A man may be silent from
          circumstances; he is taciturn from disposition. The
          loquacious man is at times silent; one who is taciturn
          may now and then make an effort at conversation.

Source : WordNet®

taciturn
     adj : habitually reserved and uncommunicative [ant: {voluble}]