Native sailor beginning to head east (9)
I believe the answer is:
aborigine
'native' is the definition.
(thesaurus)
'sailor beginning to head east' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'beginning' becomes 'origin' (origin is a kind of beginning**).
'to head' says to take the initial letters.
The initial letter of 'east' is 'e'.
'ab'+'origin'+'e'='ABORIGINE'
(Other definitions for aborigine that I've seen before include "I was in Oz first"" , "Oldest inhabitant" , "Original inhabitant" , "Native Australian" , "Early Australian" .)