Anaphylaxis
Etymology
Coined in 1902 by the French physiologist Charles Richet, with Paul Portier, from Greek “ana-” (against, or back) and “phylaxis” (protection) — literally “against protection,” the deliberate opposite of prophylaxis. They had expected repeated exposure to build immunity; instead it produced a lethal reaction. Richet won a Nobel Prize for the discovery, and the name preserves his surprise.
noun · /an-uh-fuh-LAK-sis/
A severe, whole-body allergic reaction that can swell the airways and drop blood pressure within minutes, sometimes fatally.
What it names
The emergency end of allergy — the reason a bee sting or a stray peanut can kill, and why some people carry an adrenaline injector everywhere they go.
Example
When her lips began to swell after the meal, they recognized anaphylaxis and used the adrenaline pen without waiting.
Related idea
Anaphylaxis is an allergy escalated to a systemic emergency, not merely a bad case of one. Where an ordinary reaction stays local — an itch, a rash — anaphylaxis hits the whole body at once, which is why it demands adrenaline rather than an antihistamine.