Which word indicates something that is urgent and serious?

The word "dire" effectively conveys a sense of urgency and seriousness. It is often used to describe situations that are critical or require immediate attention due to their severe implications or consequences. When something is described as "dire," it implies that the stakes are high and that action must be taken promptly to address the issue at hand.

In contrast, the other words convey very different meanings. "Trivial" suggests something that is insignificant or of little value, which does not align with a sense of urgency. "Casual" indicates a relaxed or informal approach, characterizing situations that are easygoing rather than serious. "Leisurely" also implies a slow and unhurried pace, entirely opposite to the idea of urgency. Thus, "dire" stands out as the most fitting word to describe something that is both urgent and serious.