Evening on the Arno (4)
I believe the answer is:
sera
'evening on the arno' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sera that I've seen before include "Hospital supplies" , "Sear with serums" , "Watery liquids" , "Bodily fluids (following 'que'?)" .)