Begin new existence (5)
I believe the answer is:
being
'existence' is the definition.
(synonyms)
'begin new' is the wordplay.
'new' is an anagram indicator.
'begin' with letters rearranged gives 'BEING'.
(Other definitions for being that I've seen before include "Existing" , "A living creature" , "Human, perhaps" , "See 9" , "substance" .)