under lock and key
Proposed by a contributor, not yet supported by evidence.
Where it’s used:
Used
Widespread English
Examples
Smith's copies have spent the last six days under lock and key at its Dunstable depot.
For so long she'd held the secrets of her past under lock and key, barely allowing even Kelly much more than a glimpse into her background.
British National Corpus sentence via the MAGPIE corpus (CC BY 4.0, retrieved 2026-07-30)
Sources & notes
Listed in Wiktionary’s “English idioms” category (retrieved 2026-07-29); definition pending editorial review. Definition drafted by AI (@cf/meta/llama-3.3-70b-instruct-fp8-fast) and auto-approved by rule on 2026-07-31; pending editor spot-check.
Common questions
What does “under lock and key” mean?
Kept safe and secure Literally: locked with a key
Is “under lock and key” formal or informal?
No register label has been reviewed yet — treat it as neutral and check the usage notes above.