adjective (a)

• not subject to the control of the will(adj.all)

  Example:
  Involuntary manslaughter.
  Involuntary servitude.
  An involuntary shudder.
  It (becoming a hero) was involuntary. They sank my boat.
  

  Synonym:
  nonvoluntary, unvoluntary
  Antonym:
  voluntary
  

  source: wordnet30
• controlled by the autonomic nervous system; without conscious control(adj.all)

  Example:
  Involuntary muscles.
  Gave an involuntary start.
  

  source: wordnet30
• Not having will or the power of choice.(adjective)

  source: webster1913