noun (n)

• a male demon believed to lie on sleeping persons and to have sexual intercourse with sleeping women(noun.person)

  source: wordnet30
• a situation resembling a terrifying dream(noun.state)

  Synonym:
  nightmare
  

  source: wordnet30
• someone who depresses or worries others(noun.person)

  source: wordnet30
• A demon; a fiend; a lascivious spirit, supposed to have sexual intercourse with women by night.(noun)

  source: webster1913