Top-secret (adjective)

Classified as having the highest level of security and secrecy and being available only to a select group of authorized individuals.

Origin:

20th century: from top + secret.

Examples:

1. The top-secret documents were kept in a secure location and could only be accessed by authorized personnel.
2. The top-secret information was not to be shared with anyone outside the government.
3. Only top-secret agents with high-level security clearance were allowed to attend the meeting.
4. The top-secret project was so sensitive that even its existence was kept secret.
5. The top-secret nature of the operation made it necessary to take extra precautions to ensure its success.