#cloud  any collection of particles ($('<' #physical_phenomenon replaced by #natural_object because #cloud.atmospheric_phenomenon already exists and a clous a color, a mass, ... like all natural objects)$ e.g., smoke or dust) or gases that is visible
  supertype:  natural_object__naturalobject  an object occurring naturally; not made by man
  subtype:  coma  (astronomy) the luminous cloud of particles surrounding the frozen nucleus of a comet; forms as the comet approaches the sun and is warmed
  subtype:  nebula.cloud  an immense cloud of gas (mainly hydrogen) and dust in interstellar space
     subtype:  diffuse_nebula__diffusenebula__gaseous_nebula__gaseousnebula  a cluster of stars within an intricate cloud of gas and dust
        instance:  Orion.constellation__orion__thehunter
     subtype:  planetary_nebula__planetarynebula  a nebula that was once thought to be a star with its planets but is now thought to be a very hot star surrounded by an expanding envelope of ionized gases that emit a fluorescent glow because of intense radiation from the star
  subtype:  aerosol  a cloud of solid or liquid particles in a gas
     subtype:  fog  droplets of water vapor suspended in the air near the ground
        subtype:  fogbank  a large mass of fog on the sea (as seen from a distance)
        subtype:  ice_fog__icefog__pogonip  a dense winter fog containing ice particles
        subtype:  mist  a thin fog with condensation near the ground
        subtype:  pea-souper__peasouper__pea_soup__peasoup  a heavy thick yellow fog
     subtype:  haze  atmospheric moisture or dust or smoke that causes reduced visibility
     subtype:  fume__smoke  a cloud of fine particles suspended in a gas
        subtype:  gun_smoke__gunsmoke  smoke created by the firing of guns
        subtype:  smother  a stifling cloud of smoke
  subtype:  cosmic_dust  clouds of particles or gases occurring throughout interstellar space
  subtype:  dust_cloud  a could of dust in the air
  subtype:  mushroom-shaped_cloud__mushroom__mushroom_cloud  a large cloud of rubble and dust shaped like a mushroom and rising into the sky after an explosion (especially of a nuclear bomb)

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