Fulminant (/ˈfʊlmɪnənt/) is a medical descriptor for any event or process that occurs suddenly and escalates quickly, and is intense and severe to the point of lethality, i.e., it has an explosive character.
There are several diseases described by this adjective: Beyond these particular uses, the term is used more generally as a descriptor for sudden-onset medical conditions that are immediately threatening to life or limb.
It was said of the "black death" (pneumonic bubonic plague) that some of its victims would die in a matter of hours after the initial symptoms appeared.
Cardiac arrest and stroke in certain parts of the brain, such as in the brainstem (which controls cardiovascular and respiratory system functions), and massive hemorrhage of the great arteries (such as in perforation of the walls by trauma or by sudden opening of an aneurysm of the aorta) may be very quick, causing "fulminant death".
Certain infections of the brain, such as rabies, meningococcal meningitis, or primary amebic meningoencephalitis can kill within hours to days after symptoms appear.