nimbostratus

 
Pronunciation: /ˌnɪmbə(ʊ)ˈstrɑːtəs, -ˈstreɪtəs/

noun

[mass noun]
  • cloud forming a thick uniform grey layer at low altitude, from which rain or snow often falls (without any lightning or thunder).

Origin:

late 19th century: modern Latin, from nimbus + stratus