Moor by the river bank (4)
I believe the answer is:
tier
'bank' is the definition.
(thesaurus)
'moor by the river' is the wordplay.
'moor' becomes 'tie'.
'by' says to put letters next to each other.
'the river' becomes 'r'.
'tie'+'r'='TIER'
(Other definitions for tier that I've seen before include "Wedding cake feature" , "this person secures" , "Rank - order" , "Echelon" , "Row, layer" .)