Merriam-Webster Collegiate Dictionary - cloud

 I. noun  Usage: often attributive  Etymology: Middle English, rock, ~, from Old English clud; perhaps akin to Greek gloutos buttock  Date: 14th century  1. a visible mass of particles of condensed vapor (as water or ice) suspended in the atmosphere of a planet (as the earth) or moon  2. something resembling or suggesting a ~: as  a. a light filmy, puffy, or billowy mass seeming to float in the air a ~ of blond hair a ship under a ~ of sail  b.  (1) a usually visible mass of minute particles suspended in the air or a gas  (2) an aggregation of usually obscuring matter especially in interstellar space  (3) an aggregate of charged particles (as electrons)  c. a great crowd or multitude ; swarm ~s of mosquitoes  3. something that has a dark, lowering, or threatening aspect ~s of war a ~ of suspicion  4. something that obscures or blemishes a ~ of ambiguity  5. a dark or opaque vein or spot (as in marble or a precious stone)  II. verb  Date: 1562  intransitive verb  1. to grow ~y — usually used with over or up ~ed over before the storm  2.  a. of facial features to become troubled, apprehensive, or distressed in appearance her face ~ed with worry  b. to become blurry, dubious, or ominous — often used with over the outlook is ~ing over  3. to billow up in the form of a ~  transitive verb  1.  a. to envelop or hide with or as if with a ~ smog ~ed our view  b. to make opaque especially by condensation of moisture steam ~ed the windows  c. to make murky especially with smoke or mist smoke ~ed the sky  2. to make unclear or confused ~ the issue  3. taint, sully a ~ed reputation  4. to cast gloom over ~ prospects for success