noun (n)

• noteworthy scarcity(noun.attribute)

  Synonym:
  infrequency, rareness
  

  source: wordnet30
• a rarified quality(noun.attribute)

  Synonym:
  low density, tenuity
  

  source: wordnet30
• something unusual -- perhaps worthy of collecting(noun.artifact)

  Synonym:
  curio, curiosity, oddity, oddment, peculiarity
  

  source: wordnet30
• The quality or state of being rare; rareness; thinness; as, the rarity (contrasted with the density) of gases.(noun)

  source: webster1913