key

hold the key

to provide the explanation for something that you could not previously understand. Fiennes, who had been looking for the place for twenty years, became convinced that this road held the key.

See also: hold

low-key

not intended to attract a lot of attention. She had requested that the funeral be a low-key affair. The reception itself was surprisingly low-key.

under lock and key

1. kept safely in a room or container that is locked. I tend to keep medicines under lock and key because of the kids.

2. in prison. I think the feeling from the general public is that people like that should be kept under lock and key for the rest of their lives.

See also: lock

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keyed up

nervous or excited. The interview went well today but now I'm too keyed up to sleep.

under lock and key

in a safe, protected place. The old man keeps such documents under lock and key.

See also: lock