Added 9 October 2026 niagara noun Categories: NatureRare Words noun ! Definition from WordNet 3.1, Princeton University. More about niagara at Wordnik → Where our words come from → Waterfall in Canada is the Horseshoe Falls; in the United States it is the American Falls. A river flowing from Lake Erie into Lake Ontario; forms boundary between Ontario and New York. Related Words: eriemohawkmistdelugewaterfallcataractcascadefallstorrentflood Back to today's word