Stock market purchases of endless fast runners (6)
I believe the answer is:
shares
'endless fast runners' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Maybe they are linked in a way I don't understand?
'stock market purchases' is the wordplay.
'stock' becomes 'share' (share is a kind of stock).
'market purchases' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'share'+'s'='SHARES'
'of' is the link.
Can you help me to learn more?
(Other definitions for shares that I've seen before include "Distributes, gives portions to others" , "Carves up" , "Possesses in common" , "Portions divided among a number" , "investments" .)