adj. protected by oath or vow, restricted information reserved for fellow initiates or somehow limited in general communication.
Most commonly found in usage among the various Mystery Religions in the Neo-Pagan revival today. Most of the members of Mystery Religions (like Wicca) are required to swear oaths of secrecy which limit the information which can be widely disseminated to the public at large. The secrets of the religion or the organization are restricted to only being communicated with other Initiates who have also sworn the same oath or vow. Thus, the information is 'bound' to those who are already party to the 'oath' of secrecy, thus 'oathbound'.