... longing to stock, skipping first course (4)
I believe the answer is:
ache
'longing' is the definition.
(I've seen this before)
'first course' is the wordplay.
'first' becomes 'a'.
'course' becomes 'che' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'che'='ACHE'
'to stock skipping' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for ache that I've seen before include "Throb - hurt" , "Dull throbbing pain" , "Play up" , "strong feeling" , "Dull prolonged pain" .)