To convulse means to shake violently and uncontrollably. When something convulses, it moves with sudden, jerky motions that can't be stopped or controlled easily.

The word often describes what happens during certain medical emergencies called seizures, when a person's muscles contract and relax rapidly without their control. Doctors and nurses are trained to help people who convulse, keeping them safe until the episode passes.

But convulse can also describe other kinds of violent shaking. During an earthquake, the ground itself might convulse, causing buildings to shake. A country in civil war might be described as convulsed by violence. Even laughter can make someone convulse: when something is incredibly funny, you might laugh so hard that your whole body shakes, doubling over with convulsive laughter you can't quite control.

The key idea is loss of control. Whether it's muscles, earth, or even emotions, when something convulses, it shakes with a force that overwhelms normal steadiness. Scientists use the related word convulsion as a noun to describe the shaking itself.