Professional attack — always make a quick killing (9)
I believe the answer is:
profiteer
'a quick killing' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'professional attack always' is the wordplay.
'professional' becomes 'pro' (abbreviation).
'attack' becomes 'fit' (fit is a kind of attack).
'always' becomes 'eer' (poetic way of saying ever).
'pro'+'fit'+'eer'='PROFITEER'
'make' acts as a link.
Can you help me to learn more?
(Other definitions for profiteer that I've seen before include "one who makes too much in business" , "Make too much money" , "One making excessive gains from trading" , "insider trader?" , "Gain unfairly" .)