hoarfrost

The fields were covered with hoarfrost early in the morning.

用法提示：hoarfrost 是名词，表示清晨室外物体上形成的白色冰晶。

According to the weather report, hoarfrost may form on bridges tonight.

用法提示：hoarfrost 为不可数名词，作主语，指夜间低温下形成的冰晶。

As the sun rose, the hoarfrost on the window began to melt.

用法提示：hoarfrost 作名词，用定冠词特指窗上的白霜。