Aristocrat about to drink Italian wine in citadel (7)
I believe the answer is:
bastion
'citadel' is the definition.
(synonyms)
'aristocrat about to drink italian wine' is the wordplay.
'aristocrat' becomes 'nob' (nob can mean an aristocrat).
'about' shows that the letters should be reversed in order.
'to drink' is an insertion indicator.
'italian wine' becomes 'asti' (Asti is a type of Italian wine).
'nob' reversed gives 'bon'.
'bon' going around 'asti' is 'BASTION'.
'in' acts as a link.
(Other definitions for bastion that I've seen before include "Defence - in boats (anag)" , "Obtains in fortified place or stronghold" , "Obtains (anag.)" , "part of stronghold" , "Fortified place near hostile territory" .)