Which word means not discovered or known about; uncertain?

The term "obscure" effectively captures the meaning of being not discovered or known about, as it conveys a sense of something being hidden, unclear, or not fully understood. In various contexts, when something is described as obscure, it implies that it is not well-known or easily discernible, aligning perfectly with the notion of uncertainty.

The other options do not carry the same connotation; "clear" suggests something that is easily understood or apparent, which is contrary to the idea of being uncertain. "Familiar" denotes knowledge or recognition, indicating that something is well-known rather than unknown, while "apparent" implies clarity and visibility, further diverging from the concept of uncertainty. Thus, "obscure" stands out as the most fitting choice.