in·vol·un·tar·y / inˈvälənˌterē/ • adj. 1. done without conscious control: she gave an involuntary shudder. ∎  (esp. of muscles or nerves) concerned in bodily processes that are not under the control of the will. ∎  caused unintentionally, esp. through negligence: involuntary homicide.2. done against someone's will; compulsory: a policy of involuntary repatriation.DERIVATIVES: in·vol·un·tar·i·ly / inˌvälənˈte(ə)rəlē; -ˈvälənˌter-/ adv.in·vol·un·tar·i·ness n.

involuntary (in biology) Not under the control of the will of an individual. Involuntary responses by muscles, glands, etc., occur automatically when required; many such responses, such as gland secretion, heartbeat, and peristalsis, are controlled by the autonomic nervous system and effected by involuntary muscle.

involuntary XVI. — late L.; see IN-2.