Maybe moor by river bank (4)
I believe the answer is:
tier
'bank' is the definition.
(thesaurus)
'maybe moor by river' is the wordplay.
'maybe moor' becomes 'tie'.
'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 "Rite (anag.)" , "band" , "Wedding cake layer" , "Row, level" , "Storey" .)