Ancestor warning creature in woods (8)
I believe the answer is:
forebear
'ancestor' is the definition.
(forebear is a kind of ancestor)
'warning creature in woods' is the wordplay.
'warning' becomes 'fore' (shouted in golf).
'creature in woods' becomes 'bear'.
'fore'+'bear'='FOREBEAR'
(Other definitions for forebear that I've seen before include "One of an earlier generation" , "one from the past" , "predecessor?" , "Ancestor" , "Person from whom you are descended" .)