River through Wales and England (6)
I believe the answer is:
severn
'river through wales and england' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for severn that I've seen before include "River rising in Wales" , "Gloucester's river" , "River flowing into the Bristol Channel" , "Welsh and English river" , "UK's longest river" .)