Recover strength for meeting in common cause (5)
I believe the answer is:
rally
I believe this clue is a double definition.
'recover strength' is the first definition.
(to rally is to recover one's health)
'meeting in common cause' is the second definition.
(eg a political rally)
'for' acts as a link.
(Other definitions for rally that I've seen before include "Get better; car meet" , "Muster" , "Regain health" , "Large gathering" , "Pick up" .)