DOS (d?s, dôs)n. Any of a family of operating systems that use command lines and were originally developed for personal computers made by IBM.[d(isk) o(perating) s(ystem).]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.DOS (d?s) n acronym for (Computer Science) disk-operating system, often prefixed, as in MS-DOS and PC-DOS; a computer operating systemCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014DOS (d?s, d?s) n. an operating system for microcomputers. [d(isk)o(perating)s(ystem)] DOS Department of State. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.