To cause someone to have a fever or become feverish; to afflict with fever (archaic).
From en- + fever (from Latin febris). Would have been used medically or poetically to describe the onset or intensification of fever.
Before thermometers, 'enfever' was how people described the visible transformation of fever—the flushing, the delirium—turning a symptom into an active force that was doing something to the patient.
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