Group accepts designer's ultimate label (5)
I believe the answer is:
brand
'label' is the definition.
(I know that brand is a more specific form of label)
'group accepts designer's ultimate' is the wordplay.
'group' becomes 'band' (band can mean a group of people).
'accepts' indicates putting letters inside.
'ultimate' indicates one should take the final letters (the last or ultimate letter).
The final letter of 'designer' is 'r'.
'band' going around 'r' is 'BRAND'.
(Other definitions for brand that I've seen before include "Make of product" , "Norwegian play" , "Type - it's burning" , "a particular kind" , "Label" .)