cloudy (adj.)

Old English cludig "rocky, hilly, full of cliffs;" see cloud (n.). Meaning "of the nature of atmospheric clouds" is recorded from c. 1300; meaning "full of clouds, overcast" is late 14c.; of liquids, etc., "not transparent, not clear," from 1580s. Figurative sense of "gloomy" is late 14c. Related: Cloudiness; cloudily.

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cloud nine (n.)
by 1950, sometimes also cloud seven (1956, perhaps by confusion with seventh heaven), American English, of uncertain origin or significance. Some connect the phrase with the 1895 International Cloud-Atlas (Hildebrandsson, Riggenbach and Teisserenc de Bort), long the basic source for cloud shapes, in which, of the ten cloud types, cloud No. 9, cumulonimbus, was the biggest, puffiest, most comfortable-looking. Shipley suggests the sense in this and other expressions might be because, "As the largest one-figure integer, nine is sometimes used for emphasis." The phrase might appear in the 1935 aviation-based play "Ceiling Zero" by Frank Wilbur Wead.
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Oort cloud (n.)

in reference to a hypothetical cloud of small objects beyond Pluto that become comets, proposed 1949 by Dutch astronomer Jan Hendrick Oort (1900-1992), and named for him by 1968.

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Cloud Cuckoo Land 

imaginary city built in air, 1830, translating Aristophanes' Nephelokokkygia in "The Birds" (414 B.C.E.). Cloud-land "place above the earth or away from the practical things of life, dreamland, the realm of fancy" is attested from 1840.

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nimbostratus (n.)

"thick, low, dark cloud from which rain or snow falls," 1932 (earlier use from late 19c. refers to different cloud types), from Modern Latin nimbus "cloud" (see nimbus) + connecting element -o- + stratus (see stratus). Nimbus as "a rain cloud" is attested from 1803. 

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sky (n.)

c. 1200, "a cloud," from Old Norse sky "cloud," from Proto-Germanic *skeujam "cloud, cloud cover" (source also of Old English sceo, Old Saxon scio "cloud, region of the clouds, sky;" Old High German scuwo, Old English scua, Old Norse skuggi "shadow;" Gothic skuggwa "mirror"), from PIE root *(s)keu- "to cover, conceal."

Meaning "upper regions of the air" is attested from c. 1300; replaced native heofon in this sense (see heaven). In Middle English, the word can still mean both "cloud" and "heaven," as still in the skies, originally "the clouds." Sky-high is from 1812; phrase the sky's the limit is attested from 1908. Sky-dive first recorded 1965; sky-writing is from 1922.

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Proto-Indo-European root meaning "cloud."

It forms all or part of: nebula; nebular; nebulosity; nebulous; Neptune; Nibelungenlied; Niflheim; nimbus.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit nabhas- "vapor, cloud, mists, fog, sky;" Greek nephele, nephos "cloud;" Latin nebula "mist, vapor, fog, smoke, exhalation;" German Nebel "fog;" Old English nifol "dark, gloomy;" Welsh niwl "cloud, fog;" Slavic nebo.
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Indonesian name for New Guinea, said to mean literally "cloud-covered."
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silver lining (n.)

a "bright side" which proverbially accompanies even the darkest trouble; by 1843, apparently from oft-quoted lines from Milton's "Comus," where the silver lining is the light of the moon shining from behind the cloud.

Was I deceived? or did a sable cloud
Turn forth her silver lining on the night?
I did not err, there does a sable cloud,
Turn out her silver lining on the night
And casts a gleam over this tufted grove.

To which Thomas Warton added the commentary: "When all succour ſeems to be lost, Heaven unexpectedly presents the ſilver lining oſ a ſable cloud to the virtuous."

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