1. a large waterfall or cascade, especially one of great volume and power
Usage: often used figuratively to describe a large, overwhelming flow of something
2. Niagara Falls, a famous waterfall on the border between Canada and the United States
Usage: proper noun; typically capitalized

Examples

• The dam released a niagara of water during the flood.
• Tourists from around the world visit Niagara Falls every year.
• A niagara of complaints poured in after the announcement.
• The river became a niagara as the storm intensified.
• She stood in awe before the roaring niagara of the waterfall.