adjective (a)

• not in accordance with or determined by nature; contrary to nature(adj.all)

  Example:
  An unnatural death.
  The child's unnatural interest in death.
  

  Antonym:
  natural
  

  source: wordnet30
• not normal; not typical or usual or regular or conforming to a norm(adj.all)

  Synonym:
  abnormal
  Antonym:
  normal
  

  source: wordnet30
• speaking or behaving in an artificial way to make an impression(adj.all)

  Synonym:
  affected
  Antonym:
  unaffected
  

  source: wordnet30
• Not natural; contrary, or not conforming, to the order of nature; being without natural traits; as, unnatural crimes.(adjective)

  source: webster1913