Flat piece, possibly iron, this old coin? (6)
I believe the answer is:
florin
'old coin?' is the definition.
(I've seen this before)
'flat piece possibly iron' is the wordplay.
'flat piece' becomes 'fl' (I can't justify this - if you can you should believe this answer much more).
'possibly' indicates anagramming the letters.
'iron' with letters rearranged gives 'orin'.
'fl'+'orin'='FLORIN'
'this' acts as a link.
Can you help me to learn more?
(Other definitions for florin that I've seen before include "Former British silver coin" , "Old British (or Dutch) coin" , "[SHILLINGS] ?" , "Old two-bob bit" , "An old two-shilling coin" .)