A police force operating in secrecy and outside the normal boundaries of law and hidden from the public, usually in support of a totalitarian government's political policies to suppress political dissent through the use of methods including intimidation, violence, and surveillance.

One who admires another romantically but purposely remains anonymous to the extent that the subject of the admiration is unaware of the admirer's identity.

A Christmas tradition where a group of people give anonymous gifts to each other, with each person randomly selected to give a gift to one other person.

(business) A formula, practice, process, design, instrument, pattern, or compilation of information used by a business to obtain an advantage over competitors within the same industry or profession, which kept secret from those competitors or the public.

In Australian Aboriginal culture, restricted to initiated men, or to women; not public knowledge.

The voting system involving ballots available only at official polling places, prepared at public expense, containing the names of all candidates, and marked in secret at the polling places.

(informal) Someone who is being secretive.

A revisionist interpretation of history, claimed to have been deliberately suppressed, forgotten, or ignored by established scholars.

plural of secret history

Synonym of mystery shopper