Jacket from upmarket clothing pile not fitting (5)
I believe the answer is:
unapt
'not fitting' is the definition.
(I've seen this in another clue)
'jacket from upmarket clothing pile' is the wordplay.
'jacket from' says to hollow out the word (remove centre letters) (the letters which form the word's case or jacket).
'clothing' indicates putting letters inside (some letters cover up or clothe others).
'pile' becomes 'nap' (both can refer to the surface of a fabric).
'upmarket' with its centre removed is 'ut'.
'ut' placed around 'nap' is 'UNAPT'.
(Other definitions for unapt that I've seen before include "Not fitting" , "Not qualified or suitable" , "Inappropriate" , "Not fit" , "Mentally slow" .)