Hopeless couple taken in by bad design (10)
I believe the answer is:
despairing
'hopeless' is the definition.
(similar in meaning)
'couple taken in by bad design' is the wordplay.
'couple' becomes 'pair' (synonyms).
'taken in by' means one lot of letters goes inside another.
'bad' indicates anagramming the letters.
'design' is an anagram of 'desing'.
'pair' going within 'desing' is 'DESPAIRING'.
(Other definitions for despairing that I've seen before include "hopeless" , "Losing all hope" .)