Which word means fortunate or happening by chance?

The term "fortuitous" is derived from the Latin word "fortuitus," which means accidental or happening by luck. It is used to describe events or circumstances that occur unexpectedly and, often, beneficially. In some contexts, it can refer to occurrences that happen by chance but lead to positive outcomes, emphasizing the element of favorable luck or serendipity.

In contrast, the other words carry different connotations. "Fallacy" refers to a mistaken belief or an error in reasoning, while "filibuster" describes a legislative tactic used to delay or prevent a vote. "Fickle" pertains to being changeable or inconsistent, especially with regard to loyalty or affection. Therefore, "fortuitous" stands out as the appropriate choice given its specific association with luck and chance.