Shy and dull to object return (5)
I believe the answer is:
timid
'shy' is the definition.
(I know that shy can be written as timid)
'dull to object return' is the wordplay.
'dull' becomes 'dim' (synonyms).
'to object' becomes 'it' (pronoun for an inanimate object).
'return' shows that the letters should be reversed in order.
'dim'+'it'='dimit'
'dimit' reversed gives 'TIMID'.
'and' is the link.
(Other definitions for timid that I've seen before include "Easily scared" , "Pusillanimous" , "Not assertive, retiring" , "Apprehensive and unassertive" , "doormat" .)