The question and answers posed in What is the correct way to pluralize an acronym? deals very nicely with acronym (and possibly initialism) usage. What about the case when you are defining the acronym?

For example:

  1. ...automated teller machine (ATM)... - Easy enough.
  2. ...automated teller machines (ATM)... ?
  3. ...automated teller machines (ATMs)... ?

If the singular form will be used later then option 2 seems poor. Generally option 3 appears to be best, but is it clear to the reader that we will write the singular form as "ATM"?

This idea is touched upon in Defining an acronym when using the plural of the term? but it is not complete.


2 Answers 2


I'm going to disagree with RyeBread here (sorry) -- if the acronym is a normal one in all caps, and the plural is given with a lowercase s, as in your ATMs, then your option 3 is correct - the change of case distinguishes the s from the ATM, avoiding confusion, while putting the singular form in brackets next to a plural makes it look like the singular acronym is equivalent to the plural long form. An example from my field: High-electron-mobility transistors (HEMTs), though personally I would have spelt out the long-form with initial caps. Now with the example this is too long for a comment.


My opinion is that the correct plural is ATMs which leaves room for an ATM to signal possession with an apostrophe, i.e. "Hey, this ATM's touch screen is broken."

  • 1
    ...or even These ATMs' touch screens are broken
    – Chris H
    Commented Oct 3, 2013 at 12:06

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