The antonyms for "unbriefed," which means not informed or instructed, could vary depending on the context. However, some possible opposites are "informed," "knowledgeable," "familiar," "acquainted," or "versed." These words imply that someone has received the necessary information, guidance, or training about a certain subject. They suggest that a person is aware of the risks, consequences, and objectives of their actions or decisions. Being briefed is crucial for various professionals, such as military personnel, journalists, lawyers, or diplomats, and also for anyone who wants to perform their job or duties responsibly. In summary, antonyms for "unbriefed" connote being prepared, competent, and mindful.