fortuitous

This term describes events that occur without a deliberate plan. While it technically refers to any chance occurrence, it is most frequently used in modern English to describe a lucky accident. It carries a sense of serendipity, where an unplanned event leads to a positive outcome.

In formal or legal contexts, the word may be used more neutrally to describe any accidental event, regardless of whether the result is beneficial or harmful. However, in casual conversation, using it to describe a tragedy would be unconventional and potentially confusing.