A start in life (5)
I believe the answer is:
birth
I believe this is a double definition.
'a start' is the first definition.
(birth is a kind of start)
'life' is the second definition.
(thesaurus)
'in' acts as a link.
(Other definitions for birth that I've seen before include "origin" , "Nascence" , "Nacence" , "Parentage" , "Delivery (of child)" .)