Sailor taking route overseas (6)
I believe the answer is:
abroad
'overseas' is the definition.
('abroad' can be a synonym of 'overseas')
'sailor taking route' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'taking' means one lot of letters go next to another.
'route' becomes 'road' ('road' can be a synonym of 'route').
'ab'+'road'='ABROAD'
(Other definitions for abroad that I've seen before include "At large; widely current" , "Pole would be so" , "over a wide area" , "Stare lecherously at (someone)" , "to France, maybe" .)