confidant  confident

yct01

I have only one confidant to whom I can tell my secrets.
The doctor felt confident that his patient would recover from pneumonia.

averill25

confidant n trusted person to whom one speaks about one's private affairs or secrets （可以向之披露私事或内心秘密的）知己, 密友.
confident adj ~ (of sth/that...) feeling or showing trust in oneself or one's ability 自信的; 有信心的; 有把握的:
我只有一个密友值得倾诉秘密。
医生很有把握这位病人将从肺炎中恢复。