Definition of niacin
: an acid C6H5NO2 of the vitamin B complex found widely in animals and plants and used especially against pellagra
also
: nicotinamide
— called also nicotinic acid
Buying Guide
Our Reviews team has selected the best multivitamins.
Test Your Vocabulary
Commonly Confused Words Quiz
-
- I went to the ______ store to buy a birthday card.

Can you spell these 10 commonly misspelled words?
TAKE THE QUIZ
A daily challenge for crossword fanatics.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridged
Share niacin
Time Traveler for niacin
The first known use of niacin was in 1942
See more words from the same year