Shy and dim, it retreated (5)
I believe the answer is:
timid
'shy' is the definition.
(I know that shy can be written as timid)
'dim it retreated' is the wordplay.
'retreated' shows that the letters should be reversed in order (I've seen 'retreating' mean this).
'dim'+'it'='dimit'
'dimit' in reverse letter order is 'TIMID'.
'and' is the link.
(Other definitions for timid that I've seen before include "Not assertive, retiring" , "Shrinking" , "Not brave" , "Nervous and easily alarmed" , "Apprehensive and unassertive" .)