Definition of "OS"

OS

/ˌoʊ ˈɛs/

proper noun
1. (sports) Abbreviation of Owen Sound.
2. The Ordnance Survey, official mapping agency in Great Britain (see also the noun below).
adjective
not comparable
1. Abbreviation of outsize (clothes for large people)
2. Abbreviation of oversize.
3. Abbreviation of Old Style; a term used in English language historical studies to indicate that a date conforms to the Julian calendar instead of the modern Gregorian calendar
4. (screenwriting) Abbreviation of offscreen; indicates a line of dialogue is spoken by someone not visible onscreen
adverb
not comparable
1. (Australia, informal) Abbreviation of overseas.
  Quotations
  You did the overseas trip. You went OS.
  2015, Mick Houghton, I've Always Kept a Unicorn: The Biography of Sandy Denny
  I kind of expanded my circle a bit more when I went OS [overseas].
  2022, The Betoota Advocate, The Australian Dream: Sell everything and move to Betoota, page 33
noun
plural OSes or OSs
1. (UK) an Ordnance Survey map.
2. (software) Initialism of operating system.
  Quotations
  Some vendors do now have a variant of the per-unit royalty (usually termed a “shared risk,” or similar approach), but it is not strictly the same as for those proprietary embedded OSes mentioned before […]
  2008, Karim Yaghmour, Jon Masters, Gilad Ben-Yossef, Building Embedded Linux Systems
  A policy-created scheduled task will be accepted by computers running client OSes as old as Windows 2000 […]
  2010, Jorge Orchilles, Microsoft Windows 7 Administrator's Reference
  In a dual-boot configuration, you install two OSs on the computer (Windows XP and Windows 2000, for example).
  2009, Emmett Dulaney, CompTIA A+ Complete Review Guide
3. Abbreviation of ordinary seaman.