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Synonyms

DOS

1 American  
[daws, dos] / dɔs, dɒs /

noun

Computers.

  1. any of several single-user, command-driven operating systems for personal computers, especially MS DOS.

DOS 2 American  

abbreviation

  1. Department of State.

DoS 3 American  
[daws, dos, dee-oh-es] / dɔs, dɒs, ˈdiˌoʊˈɛs /

abbreviation

  1. Computers. denial-of-service.

    DoS protection for web servers.
DOS British  
/ dɒs /

acronym

  1. disk-operating system, often prefixed, as in MS-DOS and PC-DOS; a computer operating system

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of DOS

d(isk) o(perating) s(ystem)

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Its Basic programming language and DOS operating system weren’t innovative in the market—but became standards.

From Barron's • Mar. 13, 2026

Or 5.25-inch floppies, like some of the DOS versions did.

From The Verge • Jul. 20, 2022

In the late 1990s, I was kindly, patiently coaxing senior colleagues off text-based DOS terminals and onto graphics-based Windows operating systems, wondering why they were resisting change that would make their jobs easier.

From Washington Post • May 26, 2022

We’d still be staring at DOS prompts on monochrome screens.

From Seattle Times • Nov. 20, 2021

DEFRAG, which comes standard with DOS 6.0 and later, can easily do the job.

From Debian GNU/Linux : Guide to Installation and Usage by Goerzen, John

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.