Stock exchange membership (4)
I believe the answer is:
seat
'stock exchange membership' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for seat that I've seen before include "MP's constituency" , "Box ---, position of advantage" , "Chair, bench, or stool, say" , "Constituency; location" , "A manner of sitting on horse" .)