noun, noun which may take the genitive case particle 'no'
strict secret; top-secret
Used for information that must be kept strictly confidential, often in official or formal contexts.
この書類は厳秘扱いです。
This document is treated as top-secret.
厳秘事項なので、外部に漏らさないでください。
This is a strictly confidential matter, so please do not disclose it to outsiders.