When you come across information that is unfamiliar or unclear, the phrase "not known" is typically used. However, there are several ways to convey the same meaning in writing, depending on the context and intended tone. "Unfamiliar," "obscure," or "unknown" can be used to indicate a lack of knowledge or understanding about something or someone. If you want to underscore the uncertainty or mystery of something, you might opt for words like "mysterious," "enigmatic," or "ambiguous." When the aim is to show that information is currently unavailable, "undisclosed" or "unspecified" can be used instead of "not known." Regardless of which synonym you choose, the goal should be to make your writing as clear and concise as possible.