Aesthetic quality (6)
I believe the answer is:
beauty
'aesthetic quality' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for beauty that I've seen before include "Eye-pleasing quality" , "Aesthetic quality" , "A quality pleasing to the senses" , "` `. . . . . . is only skin-deep' '" , "See 40" .)