cloud

Concise Oxford English Dictionary © 2008 Oxford University Press:
cloud/klaʊd/

▶noun

• 1 a visible mass of condensed watery vapour floating in the atmosphere, typically high above the general level of the ground.

  ■ an indistinct or billowing mass, especially of smoke or dust.

• 2 a state or cause of gloom or anxiety.

• 3 an opaque patch within a transparent substance.

▶verb

• 1 (usu. cloud over) (of the sky) become full of clouds.

• 2 make or become less clear or transparent.

• 3 make unclear or uncertain.

  ■ spoil (something).

• 4 (of the face or eyes) show sadness, anxiety, or anger.

– phrases
in (or with one's head in) the clouds out of touch with reality.
on cloud nine (or seven) extremely happy. [with ref. to a ten-part classification of clouds in which ‘nine’ was next to the highest.]
under a cloud under suspicion or discredited.

– derivatives
cloudless adjective,
cloudlessly adverb,
cloudlet noun.

word history: The earliest use of cloud is recorded in Old English, in the sense ‘a mass of rock; a hill’; from this sense arose a number of place names, such as Thorp Cloud, a hill in Derbyshire. Later it was used in the same sense as clod to mean ‘a lump of earth or clay’; indeed it is likely that cloud, clod, and clot come ultimately from the same root. The current sense, ‘mass of watery vapour’, is first recorded in a reference in the medieval work the Cursor Mundi to the sun climbing the clouds.