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 unchar 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 unchar, allowing users to choose the best word for their specific context.
Cùng học tiếng anh với từ điển Từ đồng nghĩa, cách dùng từ tương tự, Thành ngữ, tục ngữ unchar