n. A B vitamin (vitamin B₅) essential for the normal function of the nervous system and the gastrointestinal tract. Called also nicotinic acid and antipellagra vitamin. Chemical formula C6H5NO2, chemically it is 3-pyridinecarboxylic acid.
Syn. -- nicotinic acid. [ WordNet 1.5 ]

n. The amide of niacin (nicotinic acid), called also nicotinamide. It was at one time called vitamin B₃, and can function to relieve nicotinic acid deficiency. Chemical formula C6H6N2O, chemically it is 3-pyridinecarboxamide.
Syn. -- nicotinic acid amide, nicotinamide. [ PJC ]

n. lower case [ from the famous water falls. ] A large flow, used figuratively.
Syn. -- cascade. [ PJC ]

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 ]

(Geol.) A subdivision or the American Upper Silurian system, embracing the Medina, Clinton, and Niagara epoch. The rocks of the Niagara epoch, mostly limestones, are extensively distributed, and at Niagara Falls consist of about eighty feet of shale supporting a greater thickness of limestone, which is gradually undermined by the removal of the shale. See Chart of Geology. [ 1913 Webster ]

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

prop. n. The capital city of Niger. [ WordNet 1.5 ]

n. [ F. niais. See Eyas. ] A young hawk; an eyas; hence, an unsophisticated person. [ Obs. ] [ 1913 Webster ]