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1. A febrile condition in which there are alternating periods of chills, fever, and sweating. Used chiefly in reference to the fevers associated with malaria.
2. A chill or fit of shivering.
[Middle English, from Old French (fievre) ague, sharp (fever), from Medieval Latin (febris) acūta, from Latin, feminine of acūtus; see acute.]
a′gu·ish (ā′gyo͞o-ĭsh) adj.