Not very bright Italian, retiring, shy (5)
I believe the answer is:
timid
'shy' is the definition.
('timid' can be a synonym of 'shy')
'not very bright italian retiring' is the wordplay.
'not very bright' becomes 'dim' (I've seen this before).
'italian' becomes 'it'.
'retiring' says the letters should be written in reverse.
'dim'+'it'='dimit'
'dimit' back-to-front is 'TIMID'.
(Other definitions for timid that I've seen before include "Bashful or fearful" , "doormat" , "Inclined to avoid people" , "Pusillanimous" , "not forward" .)