noun (n)

• the trait of being uncommunicative; not volunteering anything more than necessary(noun.attribute)

  Synonym:
  reserve, taciturnity
  

  source: wordnet30
• 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.(noun)

  source: webster1913