#density__denseness__densenes  the amount per unit size
  supertype:  #compactness  the consistency of a compact solid
  subtype:  #relative_density  the ratio of the density of something to the density of a standard
     subtype:  #specific_gravity  the density of a substance relative to the density of water
     subtype:  #vapor_density__vapordensity__vapour_density  the density of a gas relative to the density of hydrogen
  subtype:  #rarity__tenuity__low_density__lowdensity  a rarified quality: "the tenuity of the upper atmosphere"

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