What term would best describe an unpredictable change that can happen suddenly?

The term "volatile" is most accurately used to describe an unpredictable change that can happen suddenly. In many contexts, such as finance or weather, volatility refers to the degree of variation in a subject. For instance, a volatile market can experience rapid and significant price fluctuations, while volatile weather patterns can shift quickly and dramatically, leading to unexpected storms or changes in conditions. This inherent unpredictability and tendency for swift changes make "volatile" the best descriptor for events or situations characterized by such sudden and erratic alterations.

In contrast, "stable," "calm," and "steady" connote consistency and a lack of sudden change. These terms imply a sense of order and predictability. A stable environment or situation tends to be unchanging, calm suggests tranquility with little disruption, and steady indicates reliability over time. Therefore, they serve as opposites to the notion of volatility and do not accurately capture the essence of unpredictability associated with sudden changes.