What is an injunction?

An injunction is a bidding, a command, or an order. In the world of lawyers, the legal term refers to a writ or an order from a court prohibiting a person or group from carrying out a given action, or ordering a given action to be done.

In Henry James's The American, Newman threatens the aristocratic Bellegardes with information that could destroy them:

[Mrs. Bread] has kept your secret all these years. . . . It was beneath her eyes your husband wrote that paper; he put it into her hands with a solemn injunction that she was to make it public. She was too good-hearted to make use of it.