Impose — tax (4)
I believe the answer is:
levy
I believe this is a double definition.
'impose' is the first definition.
(I know that impose can be written as levy)
'tax' is the second definition.
(I know this)
(Other definitions for levy that I've seen before include "Toll" , "Troops raised" , "Impose a tax, fine, etc" , "Impose and collect (money)" , "Tariff" .)