means A sudden violent jolt — physical, emotional, electrical, or medical — that disrupts the normal state of a body, mind, or system.

from From the French 'choc' and the verb 'choquer,' meaning to clash or collide, which English borrowed in the 1500s — originally describing the brutal moment two ranks of soldiers or two cavalry charges smashed into each other. The sense widened from that battlefield impact to any jarring blow, then to the electrical jolt (by the 1700s) and the medical emergency. The word for a thick mass of hair, as in 'a shock of hair,' is a separate, older root entirely and only collided with this one by coincidence.