Shy and stupid to object to return (5)
I believe the answer is:
timid
'shy' is the definition.
(I know that shy can be written as timid)
'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' says the letters should be written in reverse.
'dim'+'it'='dimit'
'dimit' back-to-front is 'TIMID'.
'and' acts as a link.
(Other definitions for timid that I've seen before include "Lacking self-confidence" , "Easily frightened" , "Bashful or fearful" , "doormat" , "Nervous and easily alarmed" .)