Past grads (6)
I believe the answer is:
alumni
'past grads' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alumni that I've seen before include "Past pupils, former students" , "Past pupils or graduates" , "Put too much strain on, as Revenue Commissioners do" , "Past pupils of the old school" , "we studied at a certain place" .)