a widespread outbreak of an infectious disease; many people are infected at the same time
"A severe flu epidemic swept through the city, leaving thousands of residents infected within just two weeks."
A widespread disease that affects many individuals in a population.
"The sudden outbreak of flu spread across the city, quickly becoming an epidemic that affected thousands of residents."
In plain English: An epidemic is when a disease spreads quickly to many people at once, far more than usual for that area and time.
"The flu epidemic spread quickly through our school district this winter."
Usage: Use the noun form when referring specifically to a widespread outbreak of disease, while reserving the adjective for describing non-medical phenomena like "an epidemic of gossip." Avoid confusing this term with similar words by ensuring it describes rapid spread across a population rather than just high frequency.
(especially of medicine) of disease or anything resembling a disease; attacking or affecting many individuals in a community or a population simultaneously
"an epidemic outbreak of influenza"
Like or having to do with an epidemic; widespread
"The new flu strain spread like wildfire, creating an epidemic of panic across the entire city."
In plain English: An epidemic describes something that is spreading quickly and affecting many people at once, similar to how an illness might suddenly become common everywhere.
"The epidemic-like spread of flu cases shocked the entire community."
The word comes from Ancient Greek, where it originally meant "upon the people." It is formed by combining a prefix meaning "on" with a root for "people."