Chair occupier under roof of palazzo (9)
I believe the answer is:
president
'chair' is the definition.
(eg chair or president of a board)
'occupier under roof of palazzo' is the wordplay.
'occupier' becomes 'resident' (synonyms).
'under' says to put letters next to each other.
'roof of' says to take the initial letters (in a down clue, the top letter).
The first letter of 'palazzo' is 'p'.
'resident' after 'p' is 'PRESIDENT'.
(Other definitions for president that I've seen before include "The elected head of a republic" , "authority figure" , "Wilson once" , "club official" , "Head of US company - tried pens (anag)" .)