A minor thoroughfare overseas (6)
I believe the answer is:
abroad
'overseas' is the definition.
(synonyms)
'a minor thoroughfare' is the wordplay.
'minor thoroughfare' becomes 'B road' (B road).
'a'+'broad'='ABROAD'
(Other definitions for abroad that I've seen before include "in France, say" , "on the Continent" , "Away in another country" , "Overseas; (of rumour) widely current" , "in Paris, perhaps" .)