When you are uncertain about something and lack confidence or trust in it, you are "in doubt." There are several synonyms for this phrase, including hesitant, doubtful, unsure, skeptical, and indecisive. Being apprehensive means you are skeptical of something due to conflicting thoughts or insufficient information. If you are uncertain of something, then you are unsure about it. If you are indecisive, you struggle to make a decision due to lack of information or because of conflicting thoughts. On the other hand, if you doubt something, you are questioning its validity or reliability. Therefore, for different degrees and types of uncertainties, we use different synonyms for the term "in doubt".