noun (n)

• an abnormal state in which development has stopped prematurely(noun.state)

  Synonym:
  arrested development, fixation, infantile fixation
  

  source: wordnet30
• (psychiatry) a defense mechanism in which you flee from reality by assuming a more infantile state(noun.process)

  source: wordnet30
• the relation between selected values of x and observed values of y (from which the most probable value of y can be predicted for any value of x)(noun.cognition)

  Synonym:
  regression toward the mean, simple regression, statistical regression
  

  source: wordnet30
• returning to a former state(noun.act)

  Synonym:
  regress, retrogression, retroversion, reversion
  

  source: wordnet30
• The act of passing back or returning; retrogression; retrogradation.(noun)

  source: webster1913