Tailor shortened tux carried by messenger (9)
I believe the answer is:
couturier
'tailor' is the definition.
(I know that couturier is a type of tailor)
'shortened tux carried by messenger' is the wordplay.
'shortened' means to remove the last letter.
'carried by' is an insertion indicator.
'messenger' becomes 'courier' (synonyms).
'tux' with its final letter taken off is 'tu'.
'tu' placed within 'courier' is 'COUTURIER'.
(Other definitions for couturier that I've seen before include "Designer of women's clothes" , "Top Gear producer" , "Fashion designer" .)