herald

/ˈhɛrəld/

(formal) a person who announces important news

中文释义：传令官；先驱

In medieval times, a herald would announce the arrival of the king.

在中世纪，传令官会宣布国王的到来。

The early experiments were heralds of a new era in medical science.

早期的实验预示着医学科学新时代的到来。