Meaning
Securely locked up or fastened away, whether in a literal room, safe, cabinet or prison, or figuratively for anything kept strictly controlled: 'the original manuscript is kept under lock and key'. Of a person it usually implies detention or confinement; of a thing it implies strict safeguarding or secrecy. Neutral to slightly formal; can sound emphatic or faintly figurative when applied to information rather than physical objects. Regional use: General English.
Origin
This is a plain, self-explanatory coupling of two everyday words rather than a phrase with a hidden story: it describes literally keeping something where a lock and its key control access. It has been continuously current since late Middle English: the OED's entry for the phrase, as quoted by The Free Dictionary, records slightly earlier evidence than its previous editions in a 1488-89 will of Henry Compton ('to remayn under lok and keye'), and the American Heritage Dictionary of Idioms dates the established idiom to the first half of the 1500s. The Merriam-Webster Concise Dictionary of English Usage note reproduced on the same page records that the metaphoric use, for safekeeping and imprisonment alike, dates from the 1500s and that Shakespeare used it in The Tempest (4.1). No colourful origin story attaches to it.
Research Sources
References used to check this entry’s meaning, history, or documented forms.
Variants
- Keep under lock and key
- Lock someone up and throw away the key
- Put under lock and key
Usage Examples
- The exam papers are kept under lock and key until half an hour before the test.
- Since the break-in, every power tool in the workshop is stored under lock and key.
- He has been under lock and key at the secure unit in Leeds since the ruling.