Tailored sleeve detail (6)
I believe the answer is:
gusset
'tailored sleeve detail' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for gusset that I've seen before include "Strengthening insert in garment" , "Strengthening material in a garment" , "Piece of material set into a dress" , "Piece inserted to strengthen or enlarge a garment" , "Piece inserted into garment for enlargement" .)