STRATUS
stratus, stratus cloud
(noun) a large dark low cloud
Source: WordNet® 3.1
Etymology
Noun
stratus (usually uncountable, plural strati)
(meteorology) 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; abbreviated St.
Source: Wiktionary
Stra"tus, n. Etym: [L. stratus a spreading out, scattering, from
sternere, stratum, to spread.] (Meteor.)
Definition: A form of clouds in which they are arranged in a horizontal
band or layer. See Cloud.
Source: Webster’s Unabridged Dictionary 1913 Edition