stratus

noun

Etymology: Etymology tree Proto-Indo-European *ster- Proto-Indo-European *sterh₃- Proto-Indo-European *-tós Proto-Indo-European *str̥h₃tós Proto-Italic *strātos Latin stratuslbor. English stratus Learned borrowing from Latin strātus (“spread or stretched out”). Coined by the British chemist and amateur meteorologist Luke Howard (1772–1864): see the 1803 quotation. Doublet of strath.

1. A principal, low-level cloud type in the form of a gray layer with a rather uniform base, usually not associated with precipitation, and capable of producing corona phenomena and a weak, uniform luminance.

   “[page 99] Stratus. […] A widely extended, continuous, horizontal sheet, increasing from below. […] [page 357] When a stratus covers the ground at sun-rise, however, we often see it collect into cumuli upon the evaporation of that part of it which is immediately contiguous to the earth: […]”