River through Devonshire (3)
I believe the answer is:
exe
'river through devonshire' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for exe that I've seen before include "Runner" , "Devon river" , "River in SW UK" , "River flowing from Exmoor to Exmouth via Exeter" , "Topsham's river" .)