• cloud
• 1

  in the sky

   [uncountable and countable] a white or grey mass in the sky that forms from very small drops of water
• heavy/thick/dense etc clouds
• Dark clouds floated across the moon.
• Heavy clouds had gathered over the summit of Mont Blanc.
• low/high cloud
• Visibility was bad due to low cloud.

➔ storm cloud, thundercloud

• 2

  in the air

   [countable] a mass of dust, smoke etc in the air, or a large number of insects flying together
• cloud of dust/smoke/gas etc
• A cloud of steam rose into the air
• clouds of mosquitoes buzzing around us
• 3

  problem

   [countable] something that makes you feel afraid, worried. unhappy etc
• cloud of
• the cloud of economic recession
• cloud on the horizon (=something that might spoil a happy situation)
• The only cloud on the horizon was her mother's illness.
• Fears of renewed terrorist attacks cast a cloud over the event(=spoilt the happy situation).
• He returned to New York under a cloud of gloom and despair.
• 4

   under a cloud (of suspicion)

  informal if someone is under a cloud, people have a bad opinion of them because they think they have done something wrong:
• He left the company under a cloud of suspicion.
• 5

   be on cloud nine

  informal to be very happy about something
• 6

   every cloud has a silver lining

  used to say that there is something good even in a situation that seems very sad or difficult
• 7

   be/live in cloud-cuckoo-land

  British English to think that a situation is much better than it really is, in a way that is slightly stupid

• ➔ have your head in the clouds

   at head1 (24)

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.