Academician before reversing fixed charges (5)
I believe the answer is:
rates
'charges' is the definition.
(rate is a kind of charge)
'academician before reversing fixed' is the wordplay.
'academician' becomes 'ra'.
'before' says to put letters next to each other.
'reversing' says the letters should be written in reverse.
'fixed' becomes 'set' ('set' can be a synonym of 'fixed').
'set' reversed gives 'tes'.
'ra'+'tes'='RATES'
(Other definitions for rates that I've seen before include "Taxes paid by businesses to local authority" , "Charges, deserves" , "Assesses value of - property taxation system" , "Former local taxation system" , "Fees" .)