ru·by (ro?o?b?)n. pl. ru·bies 1. A red, translucent variety of the mineral corundum, highly valued as a precious stone.2. Something, such as a watch bearing, that is made from a ruby.3. A dark or deep red to deep purplish red.adj. Of the color ruby.[Middle English, from Old French rubi, from Medieval Latin rub?nus (lapis), red (stone), ruby, from Latin rubeus, red; see reudh- in Indo-European roots.]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.ruby (?ru?b?) n, pl -bies1. (Minerals) a deep red transparent precious variety of corundum: occurs naturally in Myanmar and Sri Lanka but is also synthesized. It is used as a gemstone, in lasers, and for bearings and rollers in watchmaking. Formula: Al2O32. (Colours) a. the deep-red colour of a rubyb. (as adjective): ruby lips. 3. a. something resembling, made of, or containing a rubyb. (as modifier): ruby necklace. 4. (modifier) denoting a fortieth anniversary: our ruby wedding. 5. (Printing, Lithography & Bookbinding) (formerly) a size of printer’s type approximately equal to 5 point[C14: from Old French rubi, from Latin rubeus reddish, from ruber red] ?ruby-?like adjCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ru?by (?ru bi) n., pl. -bies, adj. n. 1. a red variety of corundum, used as a gem. 2. something made of this stone or an imitation, as a bearing in a watch. 3. a deep red; carmine. adj. 4. ruby-colored. 5. containing or set with rubies. [1275?1325; rubi (n.)