confidential
adjective
uk/ˌkɒnfɪˈdenʃəl/ usprivate, and intended to be kept secret:
confidential data/documents/information, etc. Prosecutors were not able to obtain confidential data from corporations without first receiving written approval from the department.
keep sth/remain confidential The bill would allow a business to keep its dealings confidential.
The company's former employees had made improper use of highly confidential information, such as names and addresses of customers.
All the employee questionnaires will be treated as strictly confidential.
confidential advice
The letter was marked "confidential".
confidentially
adverb uk/ˌkɒnfɪˈdenʃəli/ us/ˌkɑː–/
Members of a client's workforce can discuss confidentially the reason for their absence, be it a mental or medical problem.