An impairment or failure of normal function; a breakdown in how something is supposed to work.
From dis- (meaning 'bad' or 'abnormal') combined with function (from Latin functio, meaning 'performance' or 'duty'). The word evolved as a more technical alternative to 'dysfunction' in medical and scientific contexts.
You'll notice this is an older spelling of what we now commonly write as 'dysfunction'—the shift from 'disfunction' to 'dysfunction' shows how spelling eventually standardizes even when both forms make sense linguistically.
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