Last stop before river (6)
I believe the answer is:
endure
'last' is the definition.
(I know that last can be written as endure)
'stop before river' is the wordplay.
'stop' becomes 'end' (synonyms).
'before' says to put letters next to each other.
'river' becomes 'ure' (River Ure).
'end'+'ure'='ENDURE'
(Other definitions for endure that I've seen before include "'Last, prevail (6)'" , "Put up with or withstand" , "Last or tolerate" , "Remain in existence; suffer" , "Stand" .)