Relating to or affecting many people in a population; characteristic of an epidemic or widespread disease.
From Greek 'epidemos' (prevalent in a population) + '-ial'. This older adjective form describes epidemic phenomena, though 'epidemic' and 'epidemiological' are more commonly used today.
When a disease spreads through a population rapidly, that's epidemial—like flu season when it seems like everyone you know is sick at the same time!
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