Ague: A fever (such as from malaria) that is marked by paroxysms of chills, fever, and sweating recurring regular intervals. Also a fit of shivering, a chill. Hence, ague can refer to both chills and fevers.
Pronounced 'A-(")gyu with the accent solidly on the "A", the word "ague" is an example of how medical terminology changes with time. Not only are new terms introduced (with great speed these days) but old terms such as "ague" may decline in usage (become archaic) and eventually may be dropped entirely (be obsolete).
"Aigue" entered English usage in the 14th century, having crossed the channel from the Middle French "aguë". The word share the same origin as "acute." It descends from the Latin "acutus" meaning "sharp or pointed". A "fievre aigue" in French was a sharp or pointed (or acute) fever.