Having second thoughts means reconsidering or doubting something that was previously decided upon. Synonyms for this phrase may include questioning, reevaluating, hesitating, doubting, wavering, or changing one's mind. When someone is having second thoughts, they may be on the verge of making a different decision or taking a different course of action. They could also be expressing reservations or seeking further advice or guidance before proceeding with their original plan. It's important to pay attention to when someone is having second thoughts, as it may indicate a shift in their thinking or priorities, and could affect the outcome of the situation at hand.