The word "harbinger" refers to someone or something that announces or signals the approach of another. To choose the word that best expresses the meaning of "harbinger," we should understand and compare the meanings of the given options:
- Messenger: A person who carries a message or is employed to convey messages.
- Steward: A person responsible for managing something, such as property or a household.
- Forerunner: A sign or warning of something to come; a predecessor.
- Pilot: A person who operates the flying controls of an aircraft.
Given these definitions, "forerunner" closely aligns with the meaning of "harbinger" as it conveys the sense of a warning or sign of things to come. Therefore, the word that best expresses the meaning of "harbinger" is: