Learner's definition of CONFIDENTIAL
1 [more confidential; most confidential] : secret or private
These documents are completely/strictly confidential.
confidential medical records
Someone was leaking confidential information [=telling secrets] to the press.
2 [more confidential; most confidential] : showing that you are saying something that is secret or private
“I have something to tell you,” John said in a confidential tone/voice.
Her voice was quiet and confidential.
3 always used before a noun : trusted with secret or private information