One character inferior to another (9)
I believe the answer is:
subscript
'one character' is the definition.
(subscript is a kind of character)
'inferior to another' is the wordplay.
'inferior' becomes 'sub'.
'to another' becomes 'script' (I can't explain this - if you can you should believe this answer much more).
'sub'+'script'='SUBSCRIPT'
(Other definitions for subscript that I've seen before include "It's written below the line" , "It's written below and beside another character" , "writing this below the line" .)