niacin ni • Niagara · · · Info · Definitions · Synonyms · Characters · · niacin · · Text Latin · · Script 6 · · Length Definitions · · · (noun) a B vitamin essential for the normal function of the nervous system and the gastrointestinal tract. Synonyms: nicotinic acid. · · Noun Definition 1 Synonyms · · · nicotinic acid · · Synonym 1 Characters · · a latin small letter a U+0061 c latin small letter c U+0063 i latin small letter i U+0069 n latin small letter n U+006E