He may well strike while the iron's hot (5)
I believe the answer is:
smith
'he may well strike while' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'iron's hot' is the wordplay.
'iron's' becomes 'smit' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'hot' becomes 'h' (abbreviation eg on taps).
'smit'+'h'='SMITH'
'the' is the link.
Can you help me to learn more?
(Other definitions for smith that I've seen before include "Adam, economist" , "Common English surname" , "Forger" , "Bessie - - , blues singer" , "Person who makes things in metal, may be black" .)