Flower goes to politician in ceremony (4)
I believe the answer is:
pomp
'ceremony' is the definition.
(thesaurus)
'flower goes to politician' is the wordplay.
'flower' becomes 'po' (Italian river).
'goes to' means one lot of letters go next to another.
'politician' becomes 'mp'.
'po'+'mp'='POMP'
'in' acts as a link.
(Other definitions for pomp that I've seen before include "Stately display, goes with ceremony" , "Grandiosity" , "Ceremony and splendour" , "Stately and splendid display" , "Ostentatious ceremony" .)