Couple by river bank (4)
I believe the answer is:
tier
'bank' is the definition.
(thesaurus)
'couple by river' is the wordplay.
'couple' becomes 'tie' (I've seen this in other clues).
'by' says to put letters next to each other.
'river' becomes 'r'.
'tie'+'r'='TIER'
(Other definitions for tier that I've seen before include "Plague" , "Rite for a rank" , "Row (of seats)" , "Rite (anag.)" , "band" .)