City on the Missouri River (5)
I believe the answer is:
omaha
'city on the missouri river' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for omaha that I've seen before include "American-Indians" , "American Indian" , "- - Beach (WWII)" , "US 1944 D-Day landing beach" , "US city; D-Day 16" .)