The Collaborative International Dictionary of English v.0.48:

Taciturnity \Tac`i*tur"ni*ty\, n. [L. taciturnitas: cf. F.
   taciturnit['e].]
   Habitual silence, or reserve in speaking.
   [1913 Webster]

         The cause of Addison's taciturnity was a natural
         diffidence in the company of strangers.  --V. Knox.
   [1913 Webster]

         The taciturnity and the short answers which gave so
         much offense.                            --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

taciturnity
    n 1: the trait of being uncommunicative; not volunteering
         anything more than necessary [syn: reserve, reticence,
         taciturnity]