under lock and key

prep_phrase — 2 senses

under lock and key

prep_phrase

1

UK, US, 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.

2

UK, US, Idiomatic Safely guarded; locked away.

It is the policy of the organization to keep unused check supplies safeguarded under lock and key.2008, Edward J. McMillan, Model Policies and Procedures for Not-for-Profit Organizations, page 239:

Entry derived from the Wiktionary, under licence CC BY-SA 4.0 — list of authors.