adjective
reticent
RET-ih-sunt/ˈretɪsnt/
Inclined to hold back rather than express oneself freely.
The reticent listener stays quiet as the friendly conversation continues.

Etymology
The underlying image is keeping silent, with re- perhaps strengthening that idea. A disposition not to speak freely becomes reserve about revealing one's thoughts or feelings.
In context
He could understand that a man unable to marry should be reticent as to his feelings,--supposing him to have been weak enough to have succumbed to a passion which could only mar his own prospects.
More examples
- Maya is reticent about her childhood, even with close friends.
- Usually reticent, Ben opens up when someone asks about his garden.
- She grows more reticent whenever the discussion turns to money.
Forms
reticent · more reticent · most reticent
reticence noun — A tendency to avoid speaking freely.
reticently adverb — In a restrained or uncommunicative manner.