under lock and key
被严密保管，禁止访问或触摸
口语·强调安全保管或限制访问
英文释义
to be securely locked or closely guarded; to be kept in a safe or secure place
例句
Mom keeps all the Christmas presents under lock and key so we can't peek.
典故来源
源于中世纪，贵重物品被锁在箱子或房间里，钥匙由专人保管，确保安全。