noun (n)

• an irrational motive for performing trivial or repetitive actions, even against your will(noun.motive)

  Synonym:
  compulsion
  

  source: wordnet30
• an unhealthy and compulsive preoccupation with something or someone(noun.cognition)

  Synonym:
  fixation
  

  source: wordnet30
• The act of besieging.(noun)

  source: webster1913