Stuff awfully pure worn by composer (9)
I believe the answer is:
upholster
'stuff' is the definition.
(to upholster furniture is to give it stuffing)
'awfully pure worn by composer' is the wordplay.
'awfully' indicates an anagram.
'worn by' means one lot of letters goes inside another (outside letters are worn by those on the inside).
'composer' becomes 'holst' (Gustav Holst).
'pure' is an anagram of 'uper'.
'uper' placed around 'holst' is 'UPHOLSTER'.
(Other definitions for upholster that I've seen before include "Provide cover for" , "Provide furnishings" , "Provide furniture with padding, springs etc" , "Furnish with padding" , "Pad" .)