From Longman Dictionary of Contemporary Englishswear somebody to secrecy/silenceswear somebody to secrecy/silenceTELL A SECRETto make someone promise not to tell anyone what you have told them → swear
Examples from the Corpus
swear somebody to secrecy/silence• Amy told no one else except her younger brother Howard, and she swore him to secrecy.• Lois had sworn her to secrecy.• They swore one another to secrecy.• This time I had taken the precaution of tipping off the organizers in advance and swearing them to silence.• She swore him to secrecy and asked him to build the barrel.• He swore his family to secrecy and tried to continue living a normal life, making regular stage appearances and several movies.• No, surely he would swear her to secrecy - if he really did agree in the end to Miguel's request.• Jett swore me to secrecy, with particular reference to you. 