1.Definition: controlled by the autonomic nervous system; without conscious control

"Involuntary muscles", "Gave an involuntary start"

2.Definition: not subject to the control of the will

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

Related Adjective(s):nonvoluntary, unvoluntary