Old English clud "mass of rock, hill," related to clod. Metaphoric extension to "raincloud, mass of evaporated water in the sky" is attested by c.1200 based on similarity of cumulus clouds and rock masses. The usual Old English word for "cloud" was weolcan. In Middle English, skie also originally meant "cloud."
The four fundamental types of cloud classification (cirrus, cumulus, stratus, nimbus) were proposed by British amateur meteorologist Luke Howard (1772-1864) in 1802. Figuratively, as something that casts a shadow, from early 15c.; hence under a cloud (c.1500). In the clouds "removed from earthly things; obscure, fanciful, unreal" is from 1640s. Cloud-compeller translates (poetically) Greek nephelegereta, a Homeric epithet of Zeus.