Quality letter (9)
I believe the answer is:
character
I believe this clue is a double definition.
'quality' is the first definition.
(I know that quality can be written as character)
'letter' is the second definition.
(written character)
(Other definitions for character that I've seen before include "Distinctive nature" , "Letter or figure" , "Stamp < letter" , "I, for example" , "Quality" .)