The Collaborative International Dictionary of English v.0.48:

Reticent \Ret"i*cent\, a. [L. reticens, p. pr. of reticere to
   keep silence; re- + tacere to be silent. See Tacit.]
   Inclined to keep silent; reserved; uncommunicative.
   [1913 Webster]

WordNet (r) 3.0 (2006):

reticent
    adj 1: temperamentally disinclined to talk [syn: reticent,
           untalkative]
    2: cool and formal in manner [syn: restrained, reticent,
       unemotional]
    3: reluctant to draw attention to yourself [syn: reticent,
       self-effacing, retiring]