Make free of charge (6)
I believe the answer is:
unload
'make' is the definition.
Although both the answer and definition are verbs in their base form, I cannot see how they can define each other.
'free of charge' is the wordplay.
'free of' becomes 'un' (I can't justify this - if you can you should believe this answer much more).
'charge' becomes 'load' (synonyms).
'un'+'load'='UNLOAD'
Can you help me to learn more?
(Other definitions for unload that I've seen before include "Remove cargo from ship or charge from gun" , "Take cargo off (a ship)" , "Discharge cargo" , "Get rid" , "Remove (a gun's ammo)" .)