He does keep talking well (4)
I believe the answer is:
bore
'keep talking well' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'he does' is the wordplay.
'he' becomes 'Bo'.
'does' becomes 're' (I can't justify this - if you can you should give a lot more credence to this answer).
'bo'+'re'='BORE'
Can you help me to learn more?
(Other definitions for bore that I've seen before include "Drill - pest" , "Supported; dull person" , "Fast-running water" , "A tedious talkative person" , "Person who talks tediously" .)