Confront accountant about expenditure (6)
I believe the answer is:
accost
'confront' is the definition.
(I've seen this before)
'accountant about expenditure' is the wordplay.
'accountant' becomes 'CA' (abbreviation for chartered accountant).
'about' says the letters should be written in reverse.
'expenditure' becomes 'cost' (cost is a kind of expenditure).
'ca' backwards is 'ac'.
'ac'+'cost'='ACCOST'
(Other definitions for accost that I've seen before include "Approach and address (someone) aggressively" , "Approach boldly, solicit" , "Approach and address boldly" , "Stop and pester" , "Buttonhole" .)