(business, law) trade secret

secret admirer

medical confidentiality, doctor-patient confidentiality, doctor-patient privilege

professional secrecy, professional confidentiality

(law, banking) banking secrecy, bank confidentiality, bank privacy

open secret, secret of Polichinelle

(transitive) to hold incommunicado, to put in incommunicado detention, to put in solitary confinement

(transitive with pour) to hold no secret (for someone)

to be in the know; to have inside information, to have inside knowledge