Quarantine
Etymology
From Italian “quarantina” (about forty), from “quaranta” (forty), for the forty days that ships suspected of carrying plague were held offshore at Venice in the fourteenth century before anyone could disembark. An earlier practice used thirty days, a “trentino.” The oddly specific number, once a matter of religious symbolism and rough caution, is fossilized in the everyday word.
noun · /KWOR-uhn-teen/
A period of enforced separation for people or animals who may have been exposed to a contagious disease, whether or not they are yet sick.
What it names
The precaution aimed at the exposed-but-symptomless — a bet against the incubation period — and distinguishes it from isolating those already known to be ill.
Example
Because he had shared a flight with an infected passenger, he was placed under a two-week quarantine even though he felt perfectly well.
Related idea
Quarantine separates the possibly-exposed; isolation separates the confirmed sick. The distinction turns on the incubation period — quarantine lasts long enough to see whether a hidden infection will surface, while isolation responds to one that already has.