Which term indicates an unexpected positive occurrence?

The term that indicates an unexpected positive occurrence is "fluke." This word describes a situation where something good happens by chance or coincidence, often when it is not anticipated. For example, a person might win a lottery ticket that they bought on a whim, which would be considered a fluke because it was an unplanned, unexpected outcome that had a positive result.

In contrast, the other terms do not convey the same meaning. "Fawn" refers to exhibiting affection or flattery, typically in a submissive manner, which does not imply an unexpected occurrence. "Hackneyed" describes something that is overused or lacking originality, often used in a negative context rather than a positive one. "Grievous" denotes something that is serious or severe, perhaps even tragic, which is opposite to the idea of a positive event. Thus, "fluke" is the only term that accurately reflects an unexpected positive occurrence.