nimbostratus
noun
nim·bo·stra·tus ˌnim-bō-ˈstrā-təs 
-ˈstra-
-ˈstra- : a low dark layer of gray cloud usually producing light continuous rain or snow see cloud illustration
Example Sentences
Recent Examples on the Web Mid-level clouds are usually gray and are identified as either altocumulus, altostratus, or nimbostratus. 
Catherine Zuckerman, National Geographic, 24 Apr. 2019 Mid-level clouds are usually gray and are identified as either altocumulus, altostratus, or nimbostratus. Catherine Zuckerman, National Geographic, 24 Apr. 2019
Catherine Zuckerman, National Geographic, 24 Apr. 2019 Mid-level clouds are usually gray and are identified as either altocumulus, altostratus, or nimbostratus. Catherine Zuckerman, National Geographic, 24 Apr. 2019 Word History
Etymology
New Latin, from Latin nimbus + New Latin stratus stratus
First Known Use
circa 1909, in the meaning defined above