fu·mar·ic acid (fyo?o-m?r??k)n. A crystalline organic acid, the trans-isomer of C4H4O4, found in various plants and produced synthetically and used mainly in resins, paints, varnishes, and inks, and as a flavoring and a mordant.[From New Latin F?m?ria, genus of herbaceous plants (from Late Latin f?m?ria, fumitory, from Latin f?mus, smoke) + -ic.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.fumaric acid (fju??mær?k) n (Elements & Compounds) a colourless crystalline acid with a fruity taste, found in some plants and manufactured from benzene; trans-butenedioic acid: used esp in synthetic resins. Formula: HCOOCH:CHCOOH[C19: from New Latin Fum?ria name of genus, from Late Latin: fumitory, from Latin f?mus smoke]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014fumar?ic ac?id n. a colorless, odorless solid, C4H4O4, essential to cellular respiration in most eukaryotic organisms: used to make synthetic resins and as a replacement for tartaric acid in beverages and baking powders. [1875?80] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.