When you are not certain about something, there are several words or phrases you can use to express your uncertainty. For instance, you could use words like unsure, doubtful, skeptical, hesitant, or indecisive. If you are not entirely confident about a situation, you could use words such as apprehensive, nervous, uneasy, or anxious. Similarly, you can use ambiguous, vague, or unclear to express your lack of understanding about a topic. Additionally, uncertain can be described as tentative, ambiguous, iffy, or questionable. Whatever word you choose to use, it's always better to express your uncertainty than to act like you know something when you don't.