Assume he's a cross-country runner (3)
I believe the answer is:
don
I believe this clue is a triple definition!
'assume' is the first definition.
(I know that assume can be written as don)
'he's' is the second definition.
'a cross-country runner' is the third definition.
'Don' can be an answer for 'runner' (Yorkshire river). I'm not certain of the 'a cross-country' bit.
Can you help me to learn more?
(Other definitions for don that I've seen before include "Get into" , "Member of university" , "Bradman, the ---" , "Put on the learned man" , "Lecturer, Mafia chief and Spanish aristocrat" .)