Party, extremely grandiose, for Venice magistrate (4)
I believe the answer is:
doge
'venice magistrate' is the definition.
(as in the Doges of Venice)
'party extremely grandiose' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'grandiose' with its centre taken out is 'ge'.
'do'+'ge'='DOGE'
'for' is the link.
(Other definitions for doge that I've seen before include "Chief of ancient Venice" , "Magistrate of 14 (historical)" , "Old ruler of Venice" , "Old chief magistrate in Venice and Genoa" , "Venetian leader" .)