Altruist's concern (6)
I believe the answer is:
others
'altruist's concern' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for others that I've seen before include "Not these, alternatives" , "Not the same one already mentioned" , "Different from those already mentioned" , "Different ones" , "Not the ones already mentioned" .)