n.1 (usu. in pl.) violent irregular motion of a limb or limbs or the body caused by involuntary contraction of muscles, esp. as a disorder of infants.
2 a violent natural disturbance, esp. an earthquake.
3 violent social or political agitation.
4 (in pl.) uncontrollable laughter.
Derivatives:
convulsionary adj.
Etymology: F convulsion or L convulsio (as CONVULSE)