Wordnet 3.0
NOUN (1)
1. 
 the longest river in the United States; 
 arises in Montana and flows southeastward to become a tributary of the Mississippi at Saint Louis; 
- Example: "The Missouri and Mississippi Rivers together form the third longest river in the world"[syn: Missouri, Missouri River]
WordNet (r) 3.0 (2006):
Missouri River
    n 1: the longest river in the United States; arises in Montana
         and flows southeastward to become a tributary of the
         Mississippi at Saint Louis; "The Missouri and Mississippi
         Rivers together form the third longest river in the world"
         [syn: Missouri, Missouri River]