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 subsidiary indication.
'altered' is an anagram indicator.
'comprising' indicates putting letters inside.
'last of' suggests 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 "Clothes", "Donning clothes", "Sauce - protection for wound", "Putting clothes on", "French or vinaigrette, say", "Covering for wound; sauce for salad", "Salad sauce; a bandage", "Vinaigrette or French, say", "Bandage, plaster" and "Sauce for salads".)