ri·bose (r??b?s?)n. A pentose sugar, C5H10O5, that is a constituent of RNA and of certain vitamins and coenzymes.[German, alteration of English arabinose, a kind of sugar : (gum) arab(ic) + -in + -ose.]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.ribose (?ra?b??z; -b??s) n (Biochemistry) biochem a pentose sugar that is an isomeric form of arabinose and that occurs in RNA and riboflavin. Formula: CH2OH(CHOH)3CHO[C20: changed from arabinose]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ri?bose (?ra? bo?s) n. a white, crystalline, water-soluble, slightly sweet solid, C5H10O5, a pentose sugar obtained by the hydrolysis of RNA. [