fu·ro·se·mide (fyo?o-r??s?-m?d?)n. A white to yellow crystalline powder, C12H11ClN2O5S, used as a diuretic.[fur(fural) + s(ulf)- + alteration of amide.]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.