Fever (4)
I believe the answer is:
ague
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fever</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ague that I've seen before include "Acute fever; shivering fit" , "Old word for fever" , "Hot and cold fever" , "Fit of the shakes" , "met with cheek in Twelfth Night" .)