The Collaborative International Dictionary of English v.0.48:

Reticence \Ret"i*cence\, n. [L. reticentia: cf. F.
   r['e]ticence.]
   1. The quality or state of being reticent, or keeping
      silence; the state of holding one's tonque; refraining to
      speak of that which is suggested; uncommunicativeness.
      [1913 Webster]

            Such fine reserve and noble reticence. --Tennyson.
      [1913 Webster]

   2. (Rhet.) A figure by which a person really speaks of a
      thing while he makes a show as if he would say nothingon
      the subject.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "reticence":
   aloofness, backwardness, bashfulness, blankness, chilliness,
   coldness, constraint, coolness, detachment, discreetness,
   discretion, distance, expressionlessness, frigidity, frostiness,
   guardedness, iciness, impassiveness, impassivity, impersonality,
   inaccessibility, introversion, modesty, remoteness, repression,
   reserve, reservedness, restraint, reticency, retirement,
   standoffishness, subduedness, suppression, unaffability,
   unapproachability, uncongeniality, undemonstrativeness,
   unexpansiveness, withdrawal, withdrawnness