1. A term for a "stroke", a cerebrovascular accident (CVA), often associated with loss of consciousness and paralysis of various parts of the body.
2. Sudden impairment of neurological function; especially, something resulting from a cerebral hemorrhage.
3. Any acute clinical event, related to impairment of cerebral circulation, which lasts longer then twenty-four hours; brain attack.
4. A sudden effusion of blood into an organ or tissue.
5. A fit of extreme anger; rage.
6. Etymology: apoplexy comes from the Greek apoplexia, "a seizure", in the sense of being "struck down".

In Greek, plexe is "a stroke". The ancients believed that anyone suffering a stroke; or any sudden incapacity, had been struck down by the gods.

Also, from from Old French apoplexie, "a sudden fit of paralysis and dizziness"; or directly from Late Latin apoplexia; from apo-, "off" + plessein, "to hit".