"worst-case" is an idiom that refers to the most extreme or disastrous situation. Some synonyms for this phrase include "dire," "extreme," "catastrophic," "drastic," "terrible," "severe," "grave," "dreadful," "heartbreaking," and "appalling." Each of these words conveys a sense of urgency and seriousness, suggesting that the situation being referenced is significant and potentially dangerous. When looking for synonyms for "worst-case," it's important to consider the context and tone of the sentence, as well as the severity of the scenario being described. Ultimately, the right word choice will depend on the message the author intends to convey.