If you describe something as a bellwether, you mean that it is an indication of the way a situation is changing.
例句
For decades the company was the bellwether of the British economy...幾十年來，這家公司一直是英國經濟的晴雨表。IBM is considered the bellwether stock on Wall Street.國際商用機器公司的股票行情被視為華爾街股市的風向標。
英英詞典釋義
Noun
1. someone who assumes leadership of a movement or activity