reticence

Short definition from Wiktionary

Noun

1. 1
   Avoidance of saying or reluctance to say too much; discretion, tight-lippedness; (countable) an instance of acting in this manner.
2. 2
   A silent and reserved nature.
3. 3
   Followed by of: discretion or restraint in the use of something.
4. 4
   Often followed by to: hesitancy or reluctance (to do something).
5. 5
   Synonym of aposiopesis (“an abrupt breaking-off in speech”).

Verb

1. 1
   To deliberately not listen or pay attention to; to disregard, to ignore.