Not the whole of the dock charge (7)
I believe the answer is:
portion
'not the whole of' is the definition.
I can't judge whether this defines the answer.
'dock charge' is the wordplay.
'dock' becomes 'port' (I am not sure about this - if you are sure you should believe this answer much more).
'charge' becomes 'ion' (an ion is a charged particle).
'port'+'ion'='PORTION'
'the' is the link.
Can you help me to learn more?
(Other definitions for portion that I've seen before include "Serving" , "allotment" , "Share, helping" , "Segment" , "Amount of food" .)