noun
confidant
KON-fih-dant/ˈkɑːnfɪdænt/
A trusted person with whom private matters are shared.
The woman listens discreetly as her friend shares private matters with a trusted confidant.

Etymology
The trust root, perhaps strengthened by con-, came to describe a “trusty friend.” The modern noun focuses that trust on private affairs and secrets.
In context
She yearned, however, for a confidant. The burden of her suspicions was heavy to bear alone
More examples
- He tells his confidant about his doubts before making a decision.
- Only a few trusted confidants know her plans.
- A good confidant keeps your private conversations private.
Forms
confidant · confidants
confide verb — To share private matters with someone trusted.