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an event or period that is important because it represents a big change in how people do or think about something

(標志重大變化的)轉折點，分界線，分水嶺

The year 1969 was a watershed in her life - she changed her career and remarried.

1969年是她人生的一個轉折點——她改了行，也再婚了。

I knew that this result could be possibly a watershed moment for physicists.

我知道這一結果可能是物理學家的分水嶺。