Visitor to market, one on foot (3,3)
I believe the answer is:
big toe
'visitor' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's a link between them I don't understand?
'market one on foot' is the wordplay.
'market one on' becomes 'big' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'foot' becomes 'toe' (toeing is a kind of footing).
'big'+'toe'='BIG TOE'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for big toe that I've seen before include "that once went to market?" , "Corn grows here" , "member of the body" , "Largest pedal extremity" , "Largest foot digit" .)