Part of course: all of it except the start (4)
I believe the answer is:
hole
'part of course' is the definition.
(hole on a golf course)
'all of it except the start' is the wordplay.
'all of it' becomes 'hol' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'the start' suggests taking the first letters.
The first letter of 'except' is 'e'.
'hol'+'e'='HOLE'
Can you help me to learn more?
(Other definitions for hole that I've seen before include "Aperture; pit" , "Nasty place" , "Puncture" , "Gap; difficult situation" , "Awkward situation" .)