WordNet (r) 3.0 (2006):

DoS
    n 1: the federal department in the United States that sets and
         maintains foreign policies; "the Department of State was
         created in 1789" [syn: Department of State, United
         States Department of State, State Department, State,
         DoS]
    2: an operating system that is on a disk [syn: DOS, disk
       operating system]

The Free On-line Dictionary of Computing (19 January 2023):

DOS

    1. The common abbreviation for MS-DOS.

   2. IBM's Disk Operating System.

   3. Any disk operating system.

   (2001-03-16)