Design's altered comprising last of designer clothing (8)
I believe the answer is:
Here is my best explanation:
'clothing' is the definition.
('dress' can be a synonym of 'clothe')
'design's altered comprising last of designer' is the wordplay.
'altered' indicates an anagram.
'comprising' means one lot of letters goes inside another.
'last of' says to take the final letters.
The last letter of 'designer' is 'r'.
'designs' is an anagram of 'dessing'.
'dessing' placed around 'r' is 'DRESSING'.
(Other definitions for dressing that I've seen before include "Compress", "Clothes", "Donning clothes", "Bandage, plaster", "but not stripping!", "Putting clothes on", "Saucy thing", "clothing", "Mustard" and "Salad sauce; a bandage".)