The French outwardly vary tax (4)
I believe the answer is:
levy
'tax' is the definition.
(I've seen this before)
'the french outwardly vary' is the wordplay.
'the french' becomes 'le' ('the' in French).
'outwardly' says to hollow out the word (remove centre letters) (only the outermost letters are used).
'vary' with its middle removed is 'vy'.
'le'+'vy'='LEVY'
(Other definitions for levy that I've seen before include "Tax raised" , "Tax, fee, fine, etc" , "Toll" , "draft" , "tax money" .)