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.
This document is treated as top-secret.
This is a strictly confidential matter, so please do not disclose it to outsiders.
Compound of 厳 (gen, 'strict') and 秘 (hi, 'secret'). The exact historical derivation is uncertain, but the meaning is transparent from the kanji.