An upper member's joint (5)
I believe the answer is:
elbow
'joint' is the definition.
(joint of the body)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for elbow that I've seen before include "part of the body" , "push" , "Dismissal?" , "Arm joint, more power to it" , "Barge" .)