niacin (n.)

"pellagra-preventing vitamin in enriched bread," 1942, coined from first syllables of  nicotinic acid (see nicotine) + chemical suffix -in (2). It was suggested by the American Medical Association as a more commercially viable name than nicotinic acid.

The new name was found to be necessary because some anti-tobacco groups warned against enriched bread because it would foster the cigarette habit. ["Cooperative Consumer," Feb. 28, 1942]