Shy and stupid to object to return (5)
I believe the answer is:
timid
'shy' is the definition.
(similar in meaning)
'stupid to object to return' is the wordplay.
'stupid' becomes 'dim' (similar in meaning).
'to object' becomes 'it' (pronoun for an inanimate object).
'to return' shows that the letters should be reversed in order.
'dim'+'it'='dimit'
'dimit' written backwards gives 'TIMID'.
'and' is the link.
(Other definitions for timid that I've seen before include "Lacking self-confidence" , "Easily frightened" , "Bashful or fearful" , "doormat" , "Nervous and easily alarmed" .)