word-forming element meaning "like or of the nature of cumulus clouds," 1887, from cumulus. Cumulo-stratus is from 1803; Cumulo-nimbus is attested by 1859.
1708, "curl-like fringe or tuft," from Latin cirrus "a lock of hair, tendril, curl, ringlet of hair; the fringe of a garment." In meteorology, in reference to light, fleecy clouds, attested from 1803; so called from fancied resemblance of shape.
"slight or delicate degree of difference in expression, feeling, opinion, etc.," 1781, from French nuance "slight difference, shade of color" (17c.), from nuer "to shade," from nue "cloud," from Gallo-Roman *nuba, from Latin nubes "a cloud, mist, vapor," from PIE *sneudh- "fog" (source also of Avestan snaoda "clouds," Latin obnubere "to veil," Welsh nudd "fog," Greek nython, in Hesychius "dark, dusky").
According to Klein, the French secondary sense is a reference to "the different colors of the clouds." In reference to color or tone, "a slight variation in shade," by 1852; of music, by 1841 as a French term in English.
"a flash or gleam of light," as of the reflection of lightning on clouds or moonlight on the sea, late 15c. (Caxton, choruscacyon), from Late Latin coruscationem (nominative coruscatio), noun of action from past-participle stem of Latin coruscare "to vibrate, glitter" (see coruscate).
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.
1650s, "a heap," from Latin cumulus "a heap, pile, mass, surplus," from PIE *ku-m-olo-, suffixed shortened form of root *keue- "to swell." Meteorological use for "rounded mass of clouds, snowy white at the top with a darker, horizontal base" is attested by 1803.