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What is the correct way to pluralize an acronym?
Plural of an initialism that ends with the letter S

What is the correct plural form of an abbreviation whose last word starts with 'S' (thus making the last letter in the abbreviation an 'S')?

The example I keep running into is "CMS", an abbreviation of "Content Management System". How would I refer to a group of these beasts?

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up vote 3 down vote accepted

I think CMSes is perfectly fine. Some would say CMS's is okay, though I prefer the version without an apostrophe.

I don't agree with CMSs because CMS is an initialism where each letter is pronounced, not an acronym like SCUBA. (Though others might have input on the words initialism and acronym, you know what I mean.)

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Thanks Erik - "es" is how I've been writing it, but I keep getting told it should be "'s". – Peter Feb 23 '12 at 23:29
@Peter: You’re right. They’re wrong. You use the regular rules of English, because otherwise it won’t sound right. – tchrist Feb 23 '12 at 23:40
Personally I don't write Hes or Xes, instead writing Hs and Xs like Ps and Qs. Similarly I write Ss and so CMSs. – Henry Feb 24 '12 at 1:41
@Henry Single letters are a special case. How about your Us, As, Is, and Os? Since those are real words and thus ambiguous, I use apostrophes for single letters and follow normal rules for all others based on pronunciation. U's make me happy. Us do not. CDs are fine. OSes are not OSs (!). – ErikE Feb 24 '12 at 1:48
There are about 4X more instances of CMS's in Google than CMSes, so I'm going with CMS's google.ca/… – Mike Gifford Jan 6 at 22:37

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