The Collaborative International Dictionary of English v.0.48:

niagara \niagara\ n.

   Note: lower case [from the famous water falls.]
   A large flow, used figuratively.

   Syn: cascade.
        [PJC] Niagara

The Collaborative International Dictionary of English v.0.48:

Niagara \Niagara\, Niagara Falls \Niagara Falls\prop. n.
   A large waterfall on the Niagara River near Buffalo
   remarkable for the volume and constancy of the water flowing
   over it. That part of the waterfall in Canada is the
   Horseshoe Falls; the U. S. portion is called the American
   Falls.
   [WordNet 1.5] Niagara

The Collaborative International Dictionary of English v.0.48:

Niagara \Niagara\, Niagara River \Niagara River\prop. n.
   A river flowing from Lake Erie into Lake Ontario, which forms
   the boundary between Ontario and New York.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

Niagara
    n 1: waterfall in Canada is the Horseshoe Falls; in the United
         States it is the American Falls [syn: Niagara, Niagara
         Falls]
    2: a river flowing from Lake Erie into Lake Ontario; forms
       boundary between Ontario and New York [syn: Niagara,
       Niagara River]