Reticent is an Adjective
Meaning: Quiet, restrained, not wanting to talk
It means not sharing or revealing one's thoughts or be reluctant to speak
Noun form: Reticence
1. Ravi takes part in all discussions enthusiastically but when it comes to talking about his father he becomes reticent.
2. The new student in the class remained reticent for the first few days.
3. One of my friends is quite reticent about taking part in elocution contests.