from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A low, gray, often dark cloud that precipitates rain, snow, or sleet.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A low-level, principal cloud type, generally formless and dark grey in colour, occurring in layers at low altitude (usually below 2400 metres) and usually bringing precipitation; abbreviated Ns.
nimb(us) + stratus.(American Heritage® Dictionary of the English Language, Fourth Edition)