Financial management of company stopping incomes fluctuating (9)
I believe the answer is:
economics
'financial management' is the definition.
(I've seen this before)
'company stopping incomes fluctuating' is the wordplay.
'company' becomes 'co' (abbreviation).
'stopping' means one lot of letters goes inside another (inserted letters stop or plug a gap).
'fluctuating' indicates anagramming the letters.
'incomes' anagrammed gives 'enomics'.
'co' inserted into 'enomics' is 'ECONOMICS'.
'of' acts as a link.
(Other definitions for economics that I've seen before include "Branch of knowledge dealing with material resources" , "Treasury's concern" , "Study of the finances of the state" , "One of the social sciences" , "The study of the finances of a nation" .)