What word is used to describe an indicator or foreshadower of what is to come?

The term "harbinger" is used to describe something that indicates or foreshadows what is to come. It originates from the concept of a harbinger being a person or thing that announces or signals the arrival of something else. Often, this word is associated with the anticipation of important or notable events, suggesting that a harbinger can provide a preview or hint of future developments.

In various contexts, including literature and general discourse, a harbinger can set the tone for what is expected to follow, whether that is in a narrative, a trend in society, or changes in weather patterns. This makes it an effective word for describing indicators that signal upcoming changes or events.

The other options pertain to different meanings and contexts. "Extrapolate," for instance, refers to the act of extending conclusions based on existing data rather than indicating what is to come. "Fastidious" describes someone who is very attentive to detail or difficult to please, while "fawn" can mean to show excessive affection or flattery. None of these terms fulfill the specific meaning of foreshadowing or indicating future occurrences like "harbinger" does.