Plans to exclude a date in Italy, once (4)
I believe the answer is:
ides
'date in italy once' is the definition.
(day in the Roman calendar, as in the ides of March)
'plans to exclude a' is the wordplay.
'plans' becomes 'ideas' (idea can mean a plan or intention).
'to exclude' indicates named letters should be taken away.
'ideas' with 'a' removed is 'IDES'.
(Other definitions for ides that I've seen before include "Unlucky day for Julius Caesar" , "March day fatal to Julius Caesar" , "March 15; dies (anag.)" , "Period in month" , "Julius Caesar died in these March days" .)