under lock and key

Prepositional phrase

UK US idiomatic

Japanese Meaning

逃げる見込みがほとんどない、または全くない状態で牢に入れられている、または鍵で厳重に閉ざされた状態 / 安全に保管され、鍵でしっかりと閉ざされている状態

Ever since his capture, the notorious gangster has been kept under lock and key.

逮捕されて以来、その悪名高いギャングは逃げる可能性がほとんどない状態で収監されている。

Sense（1）

(US, UK, idiomatic) imprisoned with little or no chance of escape; locked up.

If it was him we can have him under lock and key in 24 hours.

Sense（2）

(US, UK, idiomatic) safely guarded; locked away.

It is the policy of the organization to keep unused check supplies safeguarded under lock and key.