Allergy
Etymology
Coined in 1906 by the Viennese pediatrician Clemens von Pirquet from Greek “allos” (other) and “ergon” (work or action) — literally “altered reactivity.” Von Pirquet needed a word for a puzzle: why the same substance could help the body one time and harm it another. The coinage insists that the trouble lies in the response, not in the thing itself.
noun · /AL-ur-jee/
An immune system’s exaggerated reaction to a substance that is actually harmless.
What it names
A specific kind of bodily mistake — not a poisoning or an infection, but the defenses overreacting to something innocent like peanuts, pollen, or cat dander.
Example
His allergy to shellfish was severe enough that a single bite could send him to the hospital.
Related idea
An allergy is an immune reaction; a food intolerance is a digestive one, like trouble processing lactose. People blur the two, but only an allergy can trigger anaphylaxis — an intolerance makes you uncomfortable, never breathless.