n.亂層云

A rain cloud,especially a low dark layer of clouds such as a nimbostratus. 雨云雨云，尤指象雨層云一樣的深色低云層。

A rain cloud, especially a low dark layer of clouds such as a nimbostratus. 雨云雨云，尤指象雨層云一樣的深色低云層

The lack of precipitation, other than fine drizzle, signals that it is a thin cloud, and not nimbostratus. 這種天氣降雨較少，有時下點毛毛雨，也就是說這種云比較薄，不算是雨層云。