Possibly begin living (5)
I believe the answer is:
being
'living' is the definition.
('be' can be a synonym of 'live')
'possibly begin' is the wordplay.
'possibly' is an anagram indicator.
'begin' anagrammed gives 'BEING'.
(Other definitions for being that I've seen before include "A living creature" , "Person" , "Human, perhaps" , "Living thing" , "A matter of 9 in the play" .)