Suffer knock on the head by river (6)
I believe the answer is:
endure
'suffer' is the definition.
(I know that suffer can be written as endure)
'knock on the head by river' is the wordplay.
'knock on the head' becomes 'end' (the knock something on the head is to finish it).
'by' means one lot of letters go next to another.
'river' becomes 'ure' (river in Yorkshire).
'end'+'ure'='ENDURE'
(Other definitions for endure that I've seen before include "Put up with, say hardship" , "survive" , "Stand" , "Suffer or undergo" , "Last or bear with courage" .)