More for one with small part (5)
I believe the answer is:
extra
'more' is the definition.
(I've seen this in other clues)
'one with small part' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'with' says to put letters next to each other.
'small part' becomes 'extr' (I can't explain this - if you can you should believe this answer much more).
'a' put after 'extr' is 'EXTRA'.
'for' is the link.
(Other definitions for extra that I've seen before include "not included" , "he plays his part" , "More than usual" , "One has no lines" , "Spare" .)