Key member, close (6)
I believe the answer is:
legend
'key' is the definition.
(I've seen this before)
'member close' is the wordplay.
'member' becomes 'leg' (member can mean a limb).
'close' becomes 'end' (close can mean to end or finish).
'leg'+'end'='LEGEND'
(Other definitions for legend that I've seen before include "Roger Federer, for example" , "Story from long ago" , "Old yarn" , "Ancient story" , "Saga" .)