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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

They called it JAWS, which stands for Job Access With Speech, but is also a playful reference to another DOS screen reader called Flipper, like the dolphin in an eponymous 1960s TV show.

From The Verge • Jul. 14, 2022

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

From Seattle Times • Nov. 20, 2021

Though Kreuk left the group and later stated she had “never experienced any illegal or nefarious activity,” Mack stayed on and eventually became a high-ranking leader of an all-women subgroup called DOS.

From Washington Post • Jun. 30, 2021

This usage is a recent innovation reflecting the fact that most PC clones are now delivered with DOS or Microsoft Windows pre-installed at the factory.

From The Jargon File, Version 4.0.0, 24 Jul 1996 by Raymond, Eric S.

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.