Being, existence (6)
I believe the answer is:
entity
This clue is a double definition.
'being' is the first definition.
(I've seen this in other clues)
'existence' is the second definition.
(I've seen this in another clue)
(Other definitions for entity that I've seen before include "Something existing in its own right" , "Anything that exists" , "It exists as a seperate thing (6)" , "Something with independent existence" , "Object" .)