Charge for a ring (4)
I believe the answer is:
toll
I believe this clue is a double definition.
'charge' is the first definition.
(I know that toll is a more specific form of the action impose)
'ring' is the second definition.
(a bell tolls)
'for a' acts as a link.
(Other definitions for toll that I've seen before include "repeated ringing" , "Be inclined" , "Bridge or road charge" , "Ring bell with slow strokes" , "Charge to use, eg, bridge" .)