Passage about a former coin (5)
I believe the answer is:
ducat
'former coin' is the definition.
'ducat' can be an answer for 'coin' (ducat is a kind of coin). I'm not certain of the 'former' bit.
'passage about a' is the wordplay.
'passage' becomes 'duct' (duct is a kind of passage).
'about' is an insertion indicator.
'duct' going around 'a' is 'DUCAT'.
Can you help me to learn more?
(Other definitions for ducat that I've seen before include "Antique coin" , "Old Italian coin" , "Old European gold or silver coin" , "Ancient coin" , "Former Italian gold coin" .)