/ Dictionary / Index N niacin: Meaning and Definition of Find definitions for: ni•a•cin Pronunciation: (nī'u-sin), [key] — n. Biochem. See Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: niacin (Thesaurus) NIA niacinamide Related Content Daily Word Quiz: arid Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language