How to Define Abbreviations in a Document

A listener named Paul asked about abbreviations. He wrote, 

“The guide that I was taught … was to always precede the first use of an acronym (to be placed in parenthesis) by the full term. This makes logical sense. However, if one has done this, is it then a rule that all further mentions of that same term should be replaced by the acronym (which seems logical, else, why have the acronym)?”

What Paul was taught is right.

You’d write something like this:

The World Health Organization (WHO) is headquartered in Geneva, Switzerland.

Then every time you refer to the World Health Organization later in the document, you can simply call it the WHO.

The Chicago Manual of Style has a particularly quantitative entry on the topic to help you know when to go through the effort of defining an abbreviation. Chicago Section 10.3 says if your readers aren’t likely to be familiar with the abbreviation, you should only abbreviate it if you are going to use it roughly five times or more in your document. And the book notes that you should never go through the effort of defining an abbreviation that you’re not going to use again. What would be the point? I’ve seen people do it, but I’ve always hoped that it’s because they meant to use the abbreviation again, but never got around to it.

In general, once you’ve defined an abbreviation, you should continue to use it, but one exception I’ve made in the past when I was writing long technical documents is that if I define an unfamiliar term and use it for a while, but then don’t use it for a few chapters, I’ll define it again at the beginning of a new chapter if I want to start using it again—just in case the reader forgot or took a long break from reading.

I also caution against using too many abbreviations in one document. It can be hard to know which ones to choose, but I pity the readers of some government and technical documents I’ve seen that seem to have more abbreviations than actual words. 

That’s your Quick and Dirty Tip: When you’re defining an abbreviation, write out the words first and then put the abbreviation in parentheses right afterward. Continue to use the abbreviation by itself throughout the document unless you have a good reason to define it again. And don’t get so carried away with abbreviations that your document becomes hard to read.