a colorless, crystalline, unsaturated organic acid, HOOCCH:CHCOOH, occurring in various plants or produced synthetically from maleic acid: used in making resins, as a stabilizer for foods, etc.
See fumaric acid in American Heritage Dictionary 4
(fyo͞o-mărˈĭk)
noun
An organic acid, C4H4O4, found in various plants and produced synthetically and used mainly in resins, paints, varnishes, and inks.