Depressing design and function (9)
I believe the answer is:
saddening
'depressing' is the definition.
('saddening' can be a synonym of 'depressing')
'design and function' is the wordplay.
'function' is an anagram indicator.
'design'+'and'='designand'
'designand' is an anagram of 'SADDENING'.
(Other definitions for saddening that I've seen before include "Tragic" , "Making one sorrowful" .)