1. A violent shaking of the body or limbs caused by uncontrollable muscle contractions, which can be a symptom of brain disorders and other conditions: Tom had epilepsy which caused moments of convulsions, but with his doctor’s help and medicine, he was able to control the irregular movements of his body.
2. An uncontrolled fit, as of laughter: When Jed tickled his little sister, she couldn’t help herself and was giggling and having convulsions and couldn’t stop!
3. Violent turmoil: The market convulsions of the last year have shaken the global markets and economies.
4. Etymology: from Latin convulsionem, from the past participle stem of convellere, "to tear loose"; from com-, "together" + vellere, "to pluck, to pull violently".

Relating to abnormal neuromuscular activity characterized by rapidly alternating muscle contraction and relaxation in which the contractions are intermittent and the muscles alternately contracting and relaxing.

A febrile convulsion that is prolonged; that is, longer than fifteen minutes' duratiom or is associated with focal neurological deficits.

A brief seizure, lasting less than fifteen minutes, seen in a neurologically normal infant or young child, associated with fever.

Convulsions resulting from conversion disorder (for which hysteria is an older form).

Sudden, violent movements, of the body that start soon after a severe injury: "Immediate post-traumatic convulsions result right after certain anxiety disorders have developed after exposures to some terrifying events or ordeals in which serious physical injuries have occurred."

A facial muscle spasm.

Convulsion with sustained muscle contraction.

Convulsion caused by the action of a toxin or poison on the nervous system.

A seizure associated with, or due to, an acute brain injury; such as, a concussion or contusion.