Done half of this part of the golf course (7)
I believe the answer is:
through
'done' is the definition.
('through' can be a synonym of 'done')
'half of this part of the golf course' is the wordplay.
'half of' indicates taking half.
'part of the golf course' becomes 'rough' ('rough' is part of 'golf course').
'this' cut in half is 'th'.
'th'+'rough'='THROUGH'
(Other definitions for through that I've seen before include "Using" , "Finished; by way of" , "clear" , "Non-stop - finished" , "No longer going out together" .)