Romantic piece of Italian, by Jupiter! (5)
I believe the answer is:
roman
'romantic' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
'piece of italian by jupiter' is the wordplay.
'piece' becomes 'r' (abbreviation for Rook).
'of' becomes 'o''.
'italian by jupiter' becomes 'man' (I can't justify this - if you can you should give a lot more credence to this answer).
'r'+'o'+'man'='ROMAN'
Can you help me to learn more?
(Other definitions for roman that I've seen before include "Like a type" , "Upright form of type" , "Sort of face" , "Manor (anag.)" , "One like Julius Caesar" .)