noun
: a crystalline acid C 5 H 4 NCOOH that is a member of the vitamin B complex occurring usually in the form of a complex of nicotinamide in various animal and plant parts (as blood, liver, yeast, bran, legumes), is made by oxidation of nicotine, quinoline, or methylethy pyridine, and is effective in preventing and treating human pellagra and blacktongue of dogs; 3-pyridine-carboxylic acid — called also niacin