What Are Compound Nouns?

A compound noun is a noun made of two or more words. These words work together as a single unit to name a person, place, thing, or idea.

The individual words often have their own meanings, but when combined, they create a new, specific meaning.

• Tooth (part of your mouth) + brush (a tool) = toothbrush (a tool for cleaning teeth).
• Bus (a vehicle) + stop (a place to stop) = bus stop (a place where buses stop).

How Do We Form Compound Nouns?

Compound nouns can be formed in several ways. The most common patterns involve combining two nouns or an adjective and a noun.

• Noun + Noun: This is the most frequent type. The first noun often describes or specifies the second noun. For example, football (foot + ball), bedroom (bed + room).
• Adjective + Noun: The adjective describes the noun. For example, greenhouse (green + house), blackboard (black + board).
• Verb + Noun: The verb describes the action related to the noun. For example, swimming pool (swimming + pool), washing machine (washing + machine).
• Noun + Verb: For example, sunrise (sun + rise), haircut (hair + cut).

Spelling Compound Nouns: One Word, Two Words, or Hyphenated?

The spelling of compound nouns can be tricky because there are no strict rules. They can be written in three ways:

• One word (closed): The two words are joined together. For example, keyboard, sunflower, streetlights.
• Two words (open): The words are separate. For example, bus stop, post office, road sign.
• Hyphenated: The words are joined by a hyphen. For example, sister-in-law, well-being, check-out.

Over time, some compound nouns change from two words to hyphenated, and then to one word. For example, email used to be e-mail. The best way to be sure is to check a dictionary when you are unsure.

Singular and Plural Compound Nouns

To make most compound nouns plural, you usually add -s to the main noun, which is typically the last word.

• One toothbrush → Two toothbrushes
• One bus stop → Two bus stops
• One armchair → Two armchairs

For compound nouns that are hyphenated or made of multiple words, the main noun usually takes the plural form.

• One sister-in-law → Two sisters-in-law
• One passer-by → Two passers-by

It is important to remember that the first word in a compound noun is usually singular, even if the compound noun itself is plural. For example, we say ticket office (singular) and ticket offices (plural), not tickets offices.

例

• My favourite superhero is Iron Man.
• We need to buy some new toothbrushes.
• The bus stop is just around the corner.
• She works at the post office downtown.
• Could you turn on the streetlights? It's getting dark.
• Be careful, there's a road sign missing here.
• My mother-in-law is visiting next week.
• They have a beautiful swimming pool in their garden.

練習

スペイン語話者がよく犯す間違い

Spanish speakers sometimes make mistakes with compound nouns, especially with pluralization and word order.

• Pluralizing the first word: In Spanish, it's common to make both parts of a compound plural (e.g., *coches deportivos*). However, in English, the first word of a compound noun usually stays singular, even if the compound noun is plural.
  Incorrect: I saw three tickets offices.
  Correct: I saw three ticket offices.
• Confusing adjective + noun with noun + noun: Sometimes, an adjective can look like the first part of a compound noun. Remember that the first noun in a compound noun often describes the *type* or *purpose* of the second noun, rather than just a quality. For example, economy class (noun + noun for a type of class) vs. economic crisis (adjective + noun for a quality of a crisis).

よくある質問

What is a compound noun?

A compound noun is a single noun formed by combining two or more words, like sunscreen または traffic light. It has a new, specific meaning.

Are compound nouns always written as one word?

No, compound nouns can be written as one word (bedroom), two separate words (car park), or with a hyphen (sister-in-law). You often need to check a dictionary.

How do I make a compound noun plural?

You usually add -s to the main noun, which is typically the last word. For example, two toothbrushes または two bus stops. For complex compounds, the main noun is pluralized, like sisters-in-law.

Why is the first word in a compound noun often singular?

The first word in a compound noun often acts like an adjective, describing the second word. Adjectives in English do not change for plural, so the first word stays singular, even if the entire compound noun is plural (e.g., ticket office, ticket offices).