Old iron, say (7)
I believe the answer is:
express
'say' is the definition.
(thesaurus)
'old iron' is the wordplay.
'old' becomes 'ex'.
'iron' becomes 'press' (I've seen this before).
'ex'+'press'='EXPRESS'
(Other definitions for express that I've seen before include "Fast - state - train" , "Convey; high-speed" , "set forth" , "Speak - fast" , "Utter; speedy" .)