Sold a piece of bent wire that a hot iron will melt (6)
I believe the answer is:
solder
'bent wire that a hot iron will melt' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'sold a piece' is the wordplay.
'a piece' becomes 'er' (I can't justify this - if you can you should give a lot more credence to this answer).
'sold'+'er'='SOLDER'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for solder that I've seen before include "Fusible alloy for joining metals" , "Soft alloy used to cement metals" , "Join two metal surfaces together" , "Join two metals with a melted alloy" , "Join or fuse metal, using an alloy" .)