Meaning & use
under lock and key
Last updated
Meanings
phraseidiom
Stored safely in a locked place so that nobody can get to it or remove it.
Grammar: Fixed idiom after a verb such as keep or be: the jewels are under lock and key.
Patterns
- keep something under lock and key
- be under lock and key
The museum keeps its rarest manuscripts under lock and key.
Her diary is always under lock and key.
He kept the medicine under lock and key to protect the children.
phraseidiominformal
Imprisoned or confined so that escape is impossible.
Grammar: Fixed idiom used about people held in custody: the suspect is under lock and key.
Patterns
- keep someone under lock and key
- put someone under lock and key
The thieves are finally under lock and key.
The prince was kept under lock and key in the tower.
Police said the suspect would remain under lock and key until the trial.
Common combinations
- keep under lock and key
- Keep your passport under lock and key.
- be under lock and key
- The documents are under lock and key.
- put under lock and key
- They put the prisoner under lock and key.
- safely under lock and key
- The recipe is safely under lock and key.
- remain under lock and key
- The treasure remains under lock and key.
Synonyms and how they differ
- locked away
- Locked away is more casual and literal, while under lock and key sounds more emphatic and a little formal.
- in safekeeping
- In safekeeping stresses protection and care, but not necessarily a locked container.
- behind bars
- Behind bars refers only to people in prison, while under lock and key also covers objects.
- secured
- Secured is a neutral word for made safe in any way, not only by locking.
Opposites
Word family
Commonly confused: under lock and key or under lock and key?
under lock and key vs under lock and key
Do not say under locks and keys; the idiom is fixed in the singular.
Practice
The headmaster kept the exam papers ___ until the morning of the test.
Choose one answer.
Under lock and key is the fixed idiom meaning securely locked away. The other versions change the words and are not used.
Make it your own
Write a sentence using “under lock and key”, then check it and compare it with the examples above.