Compound Nouns: What Are Compound Nouns? Definition and Examples

By Carly Forsaith, updated on August 14, 2023

Looking to learn more about compound nouns? Look no further! This article will teach you everything you need to know about compound nouns and how to use them in your writing.

In short:

  • Compound nouns are words made up of two or more separate parts that come together to form a single unit.

This guide is part of our free online Grammar Book.

What Are Compound Nouns?

Nouns are naming words, clauses, or phrases that you can use to refer to a person, place, or thing. But what about compound nouns? Grammatically, they serve the same purpose. They're just built slightly differently.

To form a compound word, you take two or more separate words and bring them together to make a new word. The great thing is that you can't only use nouns to make compound nouns; you can also use other parts of speech too. In fact, the combinations are pretty varied.

Here are some of the possibilities:

  • noun + noun (town hall)
  • verb + preposition (runoff)
  • present participle + noun (washing machine)
  • adjective + noun (shortcake)
  • preposition + noun (downtime)
  • noun + verb (haircut)

The thing to remember about compound nouns is that sometimes their meaning can be inferred from individual words (for example, a 'nosebleed' is when your nose bleeds). Still, sometimes the compound noun's meaning is seemingly completely unrelated to the individual word's meaning. For example, a 'shortcake' is not a cake that is short but a particular type of baked, layered cake.

Just like all nouns, compound nouns can be singular or plural; they can be concrete or abstract nouns. They can be possessive nouns, common, proper, or abstract.

Three Kinds of Compound Nouns

When we talk about compound nouns, we are referring to one of three kinds:

  • closed compounds
  • open compounds
  • hyphenated compounds

Let's look at each of these one by one.

Closed Compounds

  • Closed compound nouns look like just one word. In other words, they're two words merged into one; there is no space between them.

They come in almost any part of speech:

But of course, for the purposes of this article, we'll only be talking about nouns.

Here are some example sentences that use closed compound nouns:

Let's meet at the airport at 9 am.

We use floodlights to illuminate our yard during the nighttime.

I'd love to go swimming but I forgot my swimsuit at home.

How to Pluralize Closed Compounds

Closed compound nouns are the easiest type of compound to pluralize because you just need to follow the usual pluralization rules. This often involves adding an -s or -es at the end of the word, but there are many exceptions to that. You can learn more about these rules in our dedicated article on the topic.

In the meantime, here's what it looks like to pluralize a closed compound noun:

airport → airports

sweatshirt → sweatshirts

snowman → snowmen

toothbrush → toothbrushes

shellfish → shellfish

Open Compounds

With open compound nouns, you're still bringing two separate words together to form a new meaning, except when you write them, they stay as separate words. They can comprise a modifier + a noun. For example, 'hot' is an adjective, and 'dog' is a noun,' and together they make the noun 'hot dog,' which is a popular food. 'High' is an adjective, and 'school' is a noun, and together they form the noun 'high school,' a type of educational institution.

Sometimes they're formed with a verb + a noun, like in the word 'heart attack.' Though the term 'heart attack' contains two different parts of speech, a verb, and a noun, together they make a noun.

  • You can also form an open compound noun with two nouns, like with the word 'car park,' made up of the noun 'car' and the noun 'park.'

Here are some example sentences that contain open compound nouns:

Can I have a bagel with cream cheese and salmon, please?

He's old enough to start catching the school bus in the mornings.

Let's meet at the swimming pool at 2pm.

With this kind of compound, it helps to be careful; since they are made up of two separate words, you'll have to use your own judgment to decide whether it's a compound noun or just two separate words. For example, if someone mentions a 'hot dog,' are they referring to a warm animal or a popular food? You'll usually be able to tell based on the context.

How to Pluralize Open Compounds

Pluralizing open compound nouns can be slightly more complicated because it sometimes involves pluralizing the first word and sometimes the last word.

  • The trick is to find the word that is the main element of the compound—also called the 'semantic head'—and pluralize that. Let's try it out.

Take the open compound noun 'washing machine,' for example. The main word here is 'machine' since 'washing' is just a modifier to specify what kind of machine it is. Being a machine is its main trait. So we pluralize the word 'machine' and get 'washing machines.'

washing machine → washing machines

That was a case where the semantic head is the first word. Let's look at a case where the last word is the semantic head. 'Attorney general' is one such example. The fact that they are attorneys is this compound noun's most crucial aspect. 'General' is just a modifier to specify what type of attorney they are. That's why we would pluralize 'attorney' rather than 'general.'

attorney general → attorneys general

Hyphenated Compounds

The final kind of compound—hyphenated compound nouns—comprises two or more words connected by a hyphen to form a new meaning. A compound noun with more than two words is almost certainly a hyphenated compound noun.

I'm a jack-of-all-trades.

My mother-in-law is coming to visit.

I've been promoted to editor-in-chief!

  • The thing about compound words is that they can very much fluctuate between the three different types.
  • As well as this, they often change over time as they become more and more common.

As Merriam-Webster explains:

Historically, a lot of compounds follow the pattern of entering English as open compounds, then gradually take on hyphenation and eventually a closed form as they become more familiar.

Then you've got words that can be hyphenated, open or closed, like 'lifestyle'/'life style'/'life-style'. Not to mention a lack of clarity around words more recently added to the English language, like words about the internet and computing. 'Email' vs 'e-mail' and 'website' vs 'web site.'

This means there aren't hard-and-fast rules you must stick to, and you have a certain amount of creative freedom. The main thing you want to look out for is to ensure your intended meaning is clear.

How to Pluralize Hyphenated Compounds

The rules for pluralizing hyphenated compound nouns are the same as open compounds: find the semantic head, which is the principal element of the word.

Here are some examples:

take-out → take-outs

passer-by → passers-by

mother-in-law → mothers-in-law

Concluding Thoughts

That concludes this article on compound nouns. I hope you found it helpful.

Let's summarize what we've learned:

  • Compound nouns are nouns made up of two or more words that come together to form a new meaning.
  • There are three types of compound nouns: open, closed, and hyphenated.
  • When pluralizing compound nouns, look for the semantic head and pluralize that.

If you enjoyed this article, check out our Grammar Book. It's full of free grammar articles just like this one, so we thought you might like it.

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Written By:
Carly Forsaith
Carly Forsaith is one of the lead freelance writers for Carly is a copywriter who has been writing about the English language for over 3 years. Before that, she was a teacher in Thailand, helping people learn English as a second language. She is a total grammar nerd and spends her time spotting language errors on signs and on the internet.

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