noun (n)

• a poisonous or foul smelling gas emitted from the earth(noun.substance)

  source: wordnet30
• a distinctive odor that is offensively unpleasant(noun.cognition)

  Synonym:
  fetor, foetor, malodor, malodour, reek, stench, stink
  

  source: wordnet30
• in some classifications: type genus of the subfamily Mephitinae(noun.animal)

  Synonym:
  genus mephitis
  

  source: wordnet30
• Noxious, pestilential, or foul exhalations from decomposing substances, filth, or other source.(noun)

  source: webster1913