1. the falls of the Niagara River: in Canada, the Horseshoe Falls, 158 ft. (48 m) high; 2600 ft. (792 m) wide; in the U.S., American Falls, 167 ft. (51 m) high; 1000 ft. (305 m) wide.
2. a city in W New York, on the U.S. side of the falls. 71,384.
3. a city in SE Ontario, on the Canadian side of the falls. 69,423.