Fever limiting start of reasoned debate (5)
I believe the answer is:
argue
'debate' is the definition.
(I've seen this before)
'fever limiting start of reasoned' is the wordplay.
'fever' becomes 'ague' (I've seen this in other clues).
'limiting' means one lot of letters goes inside another.
'start of' indicates taking the first letters.
The first letter of 'reasoned' is 'r'.
'ague' placed around 'r' is 'ARGUE'.
(Other definitions for argue that I've seen before include "Disagree violently" , "Contend with reasoning" , "Altercate" , "express disagreement" , "Contend verbally" .)