End of binge -- endless pain for a head (4)
I believe the answer is:
each
'a head' is the definition.
(I've seen this before)
'end of binge endless pain' is the wordplay.
'end of binge' becomes 'e' (I can't justify this - if you can you should believe this answer much more).
'endless' means to remove the last letter.
'pain' becomes 'ache' (ache is a kind of pain).
'ache' with its last letter taken away is 'ach'.
'e'+'ach'='EACH'
'for' is the link.
Can you help me to learn more?
(Other definitions for each that I've seen before include "Every one of a number" , "...per head" , "Ache (anag.)" , "Singly, per capita" , "Everyone separately" .)