I have two questions which I think are so closely related that they should be grouped together.

Quantity for an abbreviation that stands for a plural

Context: The author is trying to explain what open market operations (OMO). The term "open market operation" is meaningless in the context, it is always a group of operations.

Which of the following sentences is grammatically more correct?

OMO refer to the buying or selling..........


OMO refers to the buying or selling.........

The second one is what I found in print. But I think it should be the first one.

Abbreviations that stand for the singular

Do I need to pluralize an abbreviation if it stands for the singular form?

5 kg. costs about €10.


5 kg. cost about €10.


5 kgs. cost about €10.

P.S.:- Please do let me know if the context is insufficient for the first one. Does the context even matter in such cases?

  • This "OMO", is it an organization or just a term coined for the occasion, what is it?
    – Alenanno
    Commented May 30, 2011 at 18:07
  • @Alenanno Open market operations are operations by which the Fed sells/buys US treasury in/from the secondary market (meaning normal investors such as you and me).
    – user8944
    Commented May 30, 2011 at 18:38

1 Answer 1


For the first part of your question, I would treat OMO as singular because I'd be referring to a single concept represented by that abbreviation:

  • "OMO refers to the buying or selling..."

If you were writing about a number of OMOs, then I'd use this:

  • "OMOs refer to the buying or selling..."

For the second part of your question, the first and third options are both correct, but the first is usually more appropriate instances (I also suggest changing "about" to "approximately" {or abbreviate to "approx"})...

In the scenario where I was selling 5 kg. packages of something, I prefer "5 kg. costs approximately €10."

To elaborate further, if I was selling based on weight that the buyer chooses arbitrarily, the businessman in me would prefer something along the lines of "1 kg. costs approximately €3, and for higher quantity orders 5 kg. costs approximately €10."

  • 1
    I have a follow up question on about and approx. I have seen some people use circa as well --does it fit here?
    – user8944
    Commented May 30, 2011 at 18:07
  • 1
    I don't think the third option is correct. You can't pluralize unit abbreviations, otherwise you couldn't tell if ms was meters or milliseconds. Also, it's more correct to leave off the period, e.g. "5 kg costs about €10." But otherwise I agree with this answer. Commented May 30, 2011 at 18:09
  • 3
    @MonsterTruck "circa" means "in approximately" (literally "about") but it is generally used for dates. "Jesus was born circa 4 A.D." for example. Commented May 30, 2011 at 18:09
  • 1
    @Monster Truck: "Circa" (abbreviated "c.") is typically used with dates. For example, "in c. 1980 AD the popular style of music changed drastically due to..." Commented May 30, 2011 at 18:11
  • 1
    But if I were to expand OMO to Open Market Operations then would I use the plural form?
    – user8944
    Commented May 30, 2011 at 18:12

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