Much in association with the ruling head (3)
I believe the answer is:
far
'much' is the definition.
(I've seen this in other clues)
'association with the ruling head' is the wordplay.
'association with' becomes 'fa' (I can't explain this - if you can you should give a lot more credence to this answer).
'head' indicates taking the first letters.
The first letter of 'ruling' is 'r'.
'fa'+'r'='FAR'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for far that I've seen before include "A long, long way to go" , "Very much" , "At a great distance way" , "Remote" , "Distant" .)