First and second to enter wood (8)
I believe the answer is:
foremost
'first' is the definition.
('foremost' can be a synonym of 'first')
'second to enter wood' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'to enter' means one lot of letters goes inside another.
'wood' becomes 'forest' ('forest' can be a synonym of 'wood'**).
'mo' placed into 'forest' is 'FOREMOST'.
'and' is the link.
(Other definitions for foremost that I've seen before include "'Leading, best (8)'" , "Most prominent" , "First in rank" , "Pre-eminent" , "premier" .)