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What is the correct way to pluralize an acronym?

I was answering something on Super User and wrote OSes as part of my normal flow without really thinking about it. On a re-read I decided that it didn't look right, so I changed it to OSs, which still felt incorrect. I also considered OS's, but that didn't feel right either, so I thought I'd ask on here.

In this specific case, what is the written plural form for OS?
The intention is to mean multiple Operating Systems.

And, is there a general rule for the plural form of an initialism that ends with the letter S?

  • @Noldorin - I've found this which dicusses the plural usage of acronyms. Does it also apply to initialisms? And it seems to only briefly touch upon those terminating with an S, and with contradicting views.
    – DMA57361
    Sep 22, 2010 at 12:40
  • Initialisms are a subset of acronyms, thus it fully applies. The answer given in that thread is the correct one in my view...
    – Noldorin
    Sep 22, 2010 at 15:25
  • @Noldorin - I thought acronyms were those specifically spoken as a word, for example RAM, and initialisms were not? Doesn't matter really I suppose. Anyway, the linked questions basically indicate not to use an apostrophe unless really needed, which rules out OS's. And I've decided OSs is just hideious, so OSes it is. But what about generally?
    – DMA57361
    Sep 22, 2010 at 18:02
  • @DMA573561: Wikipedia says there is no precise definition of either term (en.wikipedia.org/wiki/Initialism), but I consider initialisms to be a subset of acronyms where the letters are the first letters of each word. Acronyms and initialisms can both be spoken as words or spelled out, case by case - sometimes both are acceptable. Now if you prefer OSes, that's perfectly fine, either OSs or OSes are quite acceptable I believe.
    – Noldorin
    Sep 22, 2010 at 18:58

4 Answers 4


A search on Google for OSes returns results from several established websites such as infoworld.com, osnews.com and linux.com, which suggests OSes is the accepted form.

  • Isn't the linked question discussing words ending with S and how to write their singular possessive form? This is different from using a word to simply indicate a plural, non-possessively, isn't it? For clarity: I was referring to multiple different operating systems (there are many operating systems to choose from), not something that belonged to one operating system (the operating system's files).
    – DMA57361
    Sep 22, 2010 at 12:55
  • Doh! Sorry, you're right. I've removed the link from my post. Sep 22, 2010 at 16:44
  • 1
    I quite like 'OSes', but would be surprised to learn that it's more popular than 'OSs'.
    – J D OConal
    Sep 22, 2010 at 23:01

I disagree with Antony Quinn's assertion that just because he can find relevant results by Googling OSes this justifies calling it "valid". I don't say Google Books is an ideal "arbitration tool", but it's a lot better than a simple Internet search. I searched for:

"OSs" unix windows linux 3120 written instances

"OSes" unix windows linux 1060 instances

"OS's" unix windows linux 520 instances

That's 3:1 in favour of the "regular form" (plurals of initialisms are formed by simply adding "s").


When the word sounds like it ends in an "s" or "sh" (for example, witch /wɪtʃ/), you make it plural by adding "es."


I think the best choice would be OSes. Here's my argument:

I'm not convinced that being an acronym is of any signifcance here. I believe that the fact that it ends in 'S' is what's important. If we were talking about Political Action Committees and wanted to use its acronym in plural form, we would say PACs. I don't think there would be much debate. So, to support my answer, I'm thinking of the family name 'Jones'. Now take the sentence, "The Joneses attending the party traveled from different parts of the country." The plural, not possessive, of Jones is Joneses. I'm not completely sure but I think there's some grammatical rule about a noun in its singular form that ends in 's' is made plural by adding 'es' to the end. So, I vote for OSes.

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