If you're in uncharted waters, you are in a situation that is unfamiliar to you, that you have no experience of and don't know what might happen. ('Unchartered waters' is an incorrect form that is a common mistake.)
An charted idiom dictionary is a great resource for writers, students, and anyone looking to expand their vocabulary. It contains a list of words with similar meanings with charted, allowing users to choose the best word for their specific context.
類似の言葉の辞書、別の表現、同義語、イディオム イディオム charted