What is a Compound Noun? (Definition, Examples, How to Form)

What is a compound noun? Nouns are words that act as names of people, places, things, qualities, ideas, and actions. On the other hand, compound nouns are nouns made of two or more words, and they act as a single expression.

What is a compound noun?

A compound noun is a noun word made up of two or more words. For example, “computer keyboard” is a compound noun made up of the words “computer” and “keyboard.” To form a compound noun, you’ll put two separate words together.

Sometimes, you can do this by adding a word to the end of another word, like in the example above. Other times, you can do this by combining two words into one, as in the word “birthday,” which is made up of the words “birth” and “day.” 

You can also create compound nouns by using a hyphen, as in the word “mother-in-law,” which is made up of the words “mother” and “in-law.”

Definition of a Compound Noun

A compound noun is described as “a noun that is comprised of two or even more separate words. Such as “toothpaste”, “French fries,” or “fireflies” by the Cambridge Dictionary. The Oxford Learners’ Dictionary has the same definition.

A compound noun is defined as “an adjective, verb, or noun composed of more than two words or portions of words, expressed into one word.” Compound nouns include dark-haired, travel agent, and washroom.”

Most compound nouns follow these two structures:

• Noun + Noun
• Adjective + Noun

Verbs and prepositional phrases can also combine to form compound nouns.

Here are some examples of each type of compound noun:

Noun + Noun: Baseball, Dragonfly, Taxi-stand, Bookstore

Noun + Adjective: Town square, handful, truckful

Noun + Verb: Rainfall, haircut

Noun + Prepositional phrase: Mother-in-law, Gentleman-in-waiting

Verb + Noun: Swimsuit, Breakfast, Washing machine

Preposition + Noun: Upskill, Onlooker, Underground

Verb + Preposition: Check-out, Lookout, Go-between

Adjective + Noun: Black box, hot dog, full moon

As we can see, several combinations of words can lead to compound nouns. We use compound nouns in everyday speech and text knowingly or unknowingly.

Now, let’s see how to form sentences with them.

Sentences with compound nouns

Here are some sentences where we use compound nouns:

• That woman is my sister-in-law
• I love eating hot dogs
• The children are running around on the playground
• The pilot is trying to navigate to the runway
• She loves using the merry-go-round
• My favorite breakfast is peanut butter and jam
• Her computer’s keyboard isn’t working properly
• Greenhouse gas emission is a concern for the world
• The police are on the lookout for the criminal

Types of compound nouns

There are two ways of categorizing compound nouns. We already discussed the first way in the previous segment. Here we consider the structure of the compound noun, such as Noun + verb, Noun + Noun, adjective + Noun, and so on.

Another way of classifying compound nouns is by the number of words in the compound noun. Some compound nouns are single words, some are hyphenated words, and the remaining are disjointed words.

Single-word compound nouns are also known as closed compound nouns.

Closed compound nouns

When two words join without any hyphen or space to form a compound noun, we call it a closed compound noun. Here are some examples:

• Keyboard
• Windshield
• Parachute
• Underworld
• Haircut
• Surfboard
• Skateboard
• Whitepaper

These compound nouns include two words but without any spaces or hyphens.

Next, we have hyphenated compound nouns.

Hyphenated compound nouns

Many compound nouns are made of two or more hyphenated words. Here are some examples:

• Father-in-law
• Merry-go-round
• Lady-in-waiting
• Guard-of-honor
• X-ray
• Grown-ups
• Higher-ups

The next set of compound nouns is two words that act as single expressions. These are called open compound nouns.

Open compound nouns

Open compound nouns are two distinct words, without any hyphen or space, that act as a single noun. Here are some examples:

• Trash can
• Peanut butter
• Washing machine
• Swimming pool
• Horse racing
• Full moon
• Bus stop
• Town square
• Tennis shoe

Open compound words can be difficult to identify. The trick is to see what role the words play in the sentence. Do they represent a single thing, idea, place, name, or person? If yes, then it’s an open compound noun. If not, it could be an adjective that modifies the Noun.

Compound nouns and compound adjectives look and sound similar in text and speech. However, their roles in language are different. For example, sky-blue is a compound adjective, while black box is a compound noun. The former represents a quality (color), while the latter represents an object.

When one comes across compound adjectives and compound nouns, all they have to do is look into their function in the sentence to tell the difference.

Forming a compound noun

There are four main ways to form compound nouns:

• Join two words with a hyphen, such as “mother-in-law” or “hand-held.” 
• Join two words with a space, such as “real estate” or “full moon.” 
• Join two words with an apostrophe, such as “don’t” or “can’t.” 
• Join two words with no punctuation, such as “fireman” or “spokesperson.” 

When forming compound nouns, it is important to choose the form that is most commonly used for the particular word combination.

Compound nouns vs noun paired with other words

Since many compound nouns follow the adjective/verb + noun or noun + adjective/verb structure, we can end up confusing compound nouns with nouns painted with another word.

Here’s an example to see how it works:

• My friend lives in that green house
• The teacher taught us about the greenhouse effect today

Both sentences have the word green house, one with space and one without space. In the first sentence, green house refers to the color of the house. In the second sentence, the closed compound noun greenhouse talks about a natural phenomenon.

Here’s another example:

• My brother was playing with a white ball
• The sport of white ball cricket is slowly fading away

In the first example, the adjective white describes the noun ball. In the second sentence, white ball refers to a type of ball used in the game of cricket.

Compound noun: singular and plural

Pluralizing compound nouns is tricky. Consider the word sister-in-law. When we pluralize it, the word becomes sisters-in-law, not sister-in-laws. But when we want to pluralize the term in-law, we in-laws.

Example:

• I am going to meet my in-laws
• I have two sisters-in-law

The general rule of pluralizing compound nouns is to pluralize the semantic head, or the part of the word that conveys the primary meaning. For example, we say footballs and feetball since the object that we are talking about is a ball, not feet.

However, there are a few exceptions to this rule, such as cupful/cupfuls, and teaspoonful/teaspoonfuls. According to modern dictionaries like Merriam-Webster, cupfuls is the correct term, not cupsful.

If confused about using the plural forms of compound nouns, the best option is to refer to a dictionary to see what the plural form looks like.

Sources:

• Compound Nouns: All You Need to Know | Grammarly Blog
• Compound Nouns | Grammar | EnglishClub
• What is a Compound Noun? Examples & Exercises | Ginger (gingersoftware.com)
• What Is A Compound Noun? | Thesaurus.com