eth·a·cryn·ic acid (?th??-kr?n??k)n. A compound, C13H12Cl2O4, used as a diuretic primarily to treat severe edema.[eth(yl) + acry(lic) + (phe)n(yl) + -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.