Every initialism is an abbreviation, but most abbreviations aren’t initialisms. An abbreviation is any shortened form of a word or phrase.
An initialism is the kind built from first letters that you say one at a time, like FBI (“eff-bee-eye”). That makes the difference between an abbreviation and an initialism one of scope: one word names the family, the other names one branch.
Many people call these letter forms “acronyms.” In the strict sense, an acronym is said as a word instead of letter by letter. Dictionaries disagree on whether that strict sense still holds, and this page shows exactly where they split.
Shortened Words, Initialisms, Acronyms and Hybrids Side By Side
All four types below are abbreviations. They differ in what they’re built from and how you say them.
| Shortened word | Initialism | Acronym | Hybrid | |
| Built from | Part of one word | First letters of words or word parts | First letters, read as a word | A mix of spelled letters and a spoken word |
| How you say it | Usually as the full word | Letter by letter | As one word | Partly each way |
| Periods in Google’s style | A period at the end | None | None | None |
| Example | Apt. (apartment) | NDA (nondisclosure agreement) | NASA | JPEG |
When Saying it Out Loud Doesn’t Settle The Label
The usual test is simple. Say the abbreviation aloud: letters mean initialism, and a word means acronym.
Real abbreviations don’t always behave. These are the cases where the test wobbles, with a practical call for each.
| Example | What’s going on | What to do |
| SQL (a database language) | Usually said as three letters, but traditionally said “sequel” for Microsoft’s product | Follow your readers’ habit. Microsoft and Google both write “a SQL.” |
| VAR (soccer’s video review) | A New York Times writer pointed out that the label decides whether you say “var” or “v-a-r” | Label it by how your audience says it. |
| NCAA | Often said “N C double-A,” a shortcut through the letters | Treat it as an initialism, since you’re still naming letters. |
| TNT | The letters come from parts of one word, trinitrotoluene | American Heritage still counts it as an initialism. |
| TV | Two letters taken from a single word | Write it without periods, and make the plural TVs. |
| SAT | The letters no longer officially stand for anything | Say it by letters, and don’t try to spell it out. |
| AARP | The group dropped its full name in 1999, as Harper’s noted | Use the letters alone. |
| laser | Began as an acronym and became an ordinary lowercase word | Treat it like any everyday word. |
| i18n | The 18 stands for the letters between i and n in “internationalization” | Call it a numeronym, a letter-count shortcut. It’s neither an initialism nor an acronym. |
| Apt. | A cut-down single word, read as “apartment” | It’s an abbreviation, not an initialism. |
For anything the table doesn’t cover, work through these steps in order:
- Is it a cut-down word, like Apt. or Mon.? Call it an abbreviation and stop there.
- Is it built from first letters? Say it the way most of your readers do. Letters make it an initialism, and a word makes it an acronym.
- Do speakers split? Go with your readers’ habit, and let that same sound choose “a” or “an.”
- Do the letters stand for nothing now? Classify it by sound and skip the spelled-out form.
- Is it written in lowercase as a normal word? Treat it as a regular word with no special rules.
Is An Initialism Also An Acronym? Dictionaries Split
The honest answer depends on which reference you open. Here’s how major dictionaries and style guides treat a letter-by-letter form like NDA.
| Source | Can “acronym” cover letter-by-letter forms? | Detail |
| Merriam-Webster | Yes | Added this sense in the Collegiate 11th edition (2003). Says its research shows “acronym” commonly covers both kinds. |
| Oxford English Dictionary | Yes | Added the sense by 2011 and now lists it first. |
| American Heritage | Yes, with a warning | Labels this sense a “usage problem.” |
| Dictionary.com | Yes | Still calls the letter-by-letter meaning of “initialism” the most technical one. |
| Cambridge | No | An acronym must be said as a word. |
| Collins COBUILD | No | Defines an acronym as a word made from first letters. |
| Longman and Macmillan | No | Same narrow sense. |
| Oxford Learner’s | Keeps them apart | Defines “initialism” on its own and points to “acronym” as a contrast. |
| New Oxford American and Webster’s New World | No | Narrow sense only. |
| Chicago Manual of Style | No | Treats them as separate, while admitting the line isn’t always clear. |
| New York Times style and Garner’s usage guide | No | A form you spell out letter by letter isn’t an acronym. |
| Google developer style guide | Yes | Says calling both “acronym” is fine in most contexts. |
| Microsoft Writing Style Guide | Yes | Calls USB, FAQ and URL acronyms. |
Look at who says no. Most are learner’s dictionaries, the ones written for people studying English: Cambridge, COBUILD, Longman, Macmillan and Oxford Learner’s.
The big general dictionaries mostly moved the other way between 2003 and 2011. New Oxford American and Webster’s New World are the exceptions.
This isn’t a US-versus-UK split. The British OED accepts the broad sense, while the American New Oxford American doesn’t.
Everyday writing leans heavily toward “acronym.” In Google Books data, acronym shows up about 52 times as often as initialism in 2022. Since 1960, the gap has run from roughly 40 to 135 times, depending on the year.
Here’s a sensible middle path. Use initialism when precision matters, such as in a style guide, a lesson or an editing note. In casual writing, calling a letter-by-letter form an acronym has major dictionaries behind it.
Why “Acronym” Became The Everyday Word
“Initialism” is the older word, though the two big dictionaries don’t agree on its age. Merriam-Webster dates it to 1844, while the Oxford English Dictionary’s first print record is from 1899.
“Acronym” came later, from German. The German form appears by 1921, and the first English example comes from a 1940 translation of a novel.
That first English example used “acronym” for PGN, spelled out as “pee-gee-enn.” The letter-by-letter sense is as old as the English word itself.
“Acronym” took off in the 1960s, judging by Google Books data. The OED says “initialism” didn’t reach general use until 1965, after “acronym” had already caught on.
Merriam-Webster’s own wording has shifted, too. In 2005 it defined an initialism as a kind of acronym, and today it defines one as a kind of abbreviation.
Writing Initialisms Correctly: Articles, Plurals And Periods
“A” or “an” follows the sound, not the letter. Write an NDA, because NDA starts with the sound “en.” Microsoft and Google both prefer a SQL, while a writer who says the letters would use “an SQL.”
Plurals take a plain “s.” Write TVs and NDAs. APA and MLA both rule out an apostrophe for plurals. Keep the apostrophe for ownership, as in “the TV’s remote.” The New York Times is the outlier, since its style writes “PC’s.”
Periods depend on your style guide. Google uses no periods in initialisms. AP adds periods to most two-letter forms, like U.S., but not to EU, ID or GI. The New York Times puts periods in letter-by-letter forms, like K.G.B., but not in forms said as words.
Spell it out the first time. Give the full term, then the short form in parentheses: nondisclosure agreement (NDA). APA adds a three-use rule. If you won’t use the short form at least three times, write the full term each time. Standard, familiar short forms are the exception.
Keep the long form lowercase unless it’s a name. Google’s guide writes “data manipulation language (DML),” not “Data Manipulation Language (DML).” Capital letters in the initialism don’t make the full phrase a proper noun.
Don’t turn initialisms into verbs. Google’s guide prefers “Use SSH to log in” over “ssh into the server.”
Watch for doubled words. Editors call this redundant acronym syndrome: adding a word the letters already contain. When Trustee Savings Bank rebranded as TSB Bank, “bank” ended up in the name twice.
Don’t stack too many. AP warns against “alphabet soup,” where abbreviations pile up and slow readers down. The US federal plain-language guidelines suggest no more than three per document, and preferably two.
Where An Unclear Abbreviation Causes Real Harm
Picking the wrong label won’t hurt anyone. A misread abbreviation can.
The Joint Commission requires the health care organizations it accredits to keep a “Do Not Use” list. It created its official list in 2004, three years after a safety alert about medical abbreviations. Two entries are letter abbreviations:
- IU can be misread as IV (intravenous) or the number 10. Staff write “International Unit” instead.
- QD and QOD (daily and every other day) can be mistaken for each other. Staff write “daily” or “every other day.”
The rule covers handwritten orders, free-text computer entries and preprinted forms.
Tech writing has its own risk. Microsoft warns that in machine-translated text, short forms that spell common English words, like RAM, can come out wrong.
Government writing shows the opposite problem: defining what nobody needs defined. The federal plain-language guidelines point out that agency letters often spell out “Federal Aviation Administration (FAA)” when the name is already on the letterhead.
Can You Say “An Initialism” And “Initialisms”?
Yes. It’s an ordinary countable noun. Oxford Learner’s defines an initialism as “a word” formed from first letters. USA Today has written that “acronyms, initialisms and slang” can shorten our conversations.
You’re always safe calling a shortened form an abbreviation. Reach for initialism when you want to say exactly how the letters are spoken, and let that same sound decide between “a” and “an.”
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I’m Hazel, and I studied BSC English at GCUF. I focus on explaining word meanings in simple, clear language that anyone can understand. My goal is helping readers grasp everyday English, confusing terms, and slang used in real conversations and social media. I believe language learning works best when definitions connect to actual life situations. Through careful research and straightforward explanations, I make vocabulary accessible for students, learners, and anyone curious about how English really works in daily use.