[气] cumulonimbus (cloud) ；

[例句] 天上几乎已是一片乌黑, 布满了一团团怕人的浓浓的积雨云. It was almost black, dotted with ugly leaden rain clouds.

[例句] 黑压压的积雨云低垂在墨西哥湾上空. Black storm clouds were low and heavy over the Gulf.