silent

be as silent as the grave (literary)

to be completely silent. It was four o'clock in the morning and London was as silent as the grave.

See also: grave

the silent majority

the large numbers of people in a country or group who do not express their opinions publicly. What does the silent majority expect from a new Labour government?

sleeping partner (British, American & Australian)

someone who is closely involved with a company, and often provides money for it, but is not a manager of it. He was an extremely wealthy man, and she was hoping he might become a sleeping partner in their new vineyards.

See also: partner, sleep