How to pluralise compound nouns in English

Estimated reading time: 4 minutes

Pluralizing nouns in English can be straightforward—just add an “-s” or “-es” at the end of the word. But when it comes to compound nouns, things can get a little tricky.

A compound noun is made up of two or more words that together create a new meaning, like “mother-in-law,” “toothbrush,” or “editor-in-chief.”

In today’s NRTC English, I have explained how to correctly pluralize compound nouns, starting with the simplest forms and moving on to more complex examples. Besides, I have also provided ample exceptions to these rules.

1. Basic Rule: Add -s or -es

For compound nouns that are written as one word, you generally add an “-s” or “-es” at the end, just like you would with a simple noun.

Examples:

• toothbrush → toothbrushes
• notebook → notebooks
• raincoat → raincoats

Here, the whole word is treated as a single entity, so the plural marker goes at the end of the word.

2. Hyphenated Compound Nouns

When dealing with hyphenated compound nouns (words connected by hyphens), the key is to identify the most important part of the noun, usually the one that carries the primary meaning (in the sense that it is the substance or life of the compound noun). This part is called the head noun. The plural marker is then added to this head noun.

Examples:

• mother-in-law → mothers-in-law
• runner-up → runners-up
• editor-in-chief → editors-in-chief

In these cases, the plural “-s” is added to the word that represents the main subject of the compound noun, not at the end.

3. Open Compound Nouns

Open compound nouns are written as separate words, but they work together to express a single idea, like “attorney general” or “court-martial.” To pluralize these, you again focus on the head noun.

Examples:

• attorney general → attorneys general
• passerby → passersby
• court-martial → courts-martial

Notice that the noun carrying the central meaning (e.g., “attorney,” “passer,” “court”) gets pluralized, while the other word remains unchanged.

4. Irregular Plurals

Some compound nouns have irregular plurals, meaning they don’t follow the usual “-s” or “-es” rules. For example, “man” becomes “men,” and “woman” becomes “women.”

Examples:

• man-of-war → men-of-war
• woman doctor → women doctors
• manservant → menservants

In these cases, the entire head noun changes form in the plural, rather than just adding “-s” or “-es.”

5. Compound Nouns with Numbers or Letters

Sometimes, compound nouns include numbers, letters, or abbreviations, which require special consideration when forming plurals.

Examples:

• CD player → CD players
• T-shirt → T-shirts
• two-year-old → two-year-olds

Here, the main noun (like “player” or “T-shirt”) receives the plural marker, not the number or letter.

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Compound Nouns with Variable Plurals

Sometimes, compound nouns can have more than one correct plural form, and the choice between them can depend on context, regional usage, or preference.

Examples:

• court-martial → courts-martial or court-martials
• attorney general → attorneys general or attorney generals

Both forms are often correct, and usage might vary depending on the region or specific context. For example, British English is more likely to use “courts-martial” as the plural form. Also, in British English, the plural “attorneys general” is more commonly used.

Similarly, “attorney generals” might be used in American English, although “attorneys general” remains standard.

In American English, “court-martials” is increasingly accepted alongside “courts-martial”.

Multiple Choice Questions

In the options lettered A-D, identify the correct plural forms of the underlined words.

1. The dentist advised that we should replace our old toothbrush every three months.
A. Toothbrushs
B. Toothbrushes
C. Toothbrushies
D. Toothbrush

2. During the holiday, all the mother-in-law were invited to the family reunion.
A. Mother-in-laws
B. Mothers-in-law
C. Mothers-in-laws
D. Mother-in-lawses

3. The president met with the attorney general of several states to discuss the new law.
A. Attorney generals
B. Attorneys generals
C. Attorney general
D. Attorneys general

4. Several passerby stopped to watch the street performance.
A. Passerbys
B. Passersby
C. Passersbys
D. Passerbyes

5. The mansion was well-staffed with loyal manservant.
A. Mansservants
B. Menservants
C. Manservants
D. Mansservant