There are several synonyms that can be used for the phrase "not well-known". Some commonly used alternatives could be obscure, unfamiliar, little-known, unknown, or unnoticed. These words can be used to describe something that is not widely recognized or familiar to a large audience. The use of these synonyms can help to add variety and depth to written or spoken language by avoiding repetition and adding nuance to a sentence. Additionally, these words can be used to describe a vast array of objects, places, or people that may not be familiar to a wider audience due to geographic or cultural limitations.