"At worst" is a phrase used to describe a situation where the outcome is as bad as it can be. It is often used to provide perspective on a situation, as in "at worst, we'll lose some money." However, there are several synonyms that can be used instead of "at worst." For example, "in the worst-case scenario" is a common synonym that is often used in business or legal settings. "In the worst possible situation" is another similar phrase that can be used in casual speech. Ultimately, the choice of synonym will depend on the context and tone of the conversation.