Where Does the 'S' Go? Forming Plural Compound Nouns

Contributor: Allison Crews. Lesson ID: 13721

Pluralizing compound nouns can be tricky, but the simple rules in this lesson will help you know how to handle them.


Grammar, Writing

English / Language Arts
learning style
personality style
Lion, Otter
Grade Level
High School (9-12)
Lesson Type
Quick Query

Lesson Plan - Get It!

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Here's one of the trickiest examples of pluralizing compound nouns:


sister in law

  • How would you pluralize that?

Write your answer down and find out if you're correct later in the lesson!

In order to learn the rules of pluralizing compound nouns, you first must understand what compound nouns are.

A compound noun is two or more words that, together, form a single noun. There are three types:

  • open or separated (space between words)

examples: full moon, car seat, dining room

  • hyphenated (hyphens between words)

examples: sister-in-law, self-esteem, runner-up

  • closed or combined (all one word)

examples: seafood, lumberjack, bedroom


On paper, make a three-column list. Write down as many examples as you can think of for each type of compound noun.

How Are Compound Nouns Formed?

There are various word part combinations that can be used to make compound nouns.

The most common are:

noun + noun

adjective + noun

However, there are many others. For example:

  verb + noun verb + preposition
  noun + verb preposition + verb
  adjective + noun preposition + noun


Compound nouns are an area of grammar where it is easy to see how things shift over time. For example, the compound noun snowman was snow man for a long time before becoming a combined compound noun.

  • So how do you know what to do with a compound noun?

There is a process that can help.

Using your favorite word processing application, type a compound word as combined to see if the grammar or spell check accepts it as correct.

If it doesn't, you'll need to do some research to find out if hyphenating is correct.

Word processors generally treat hyphens as spaces, so the first trick won't work. You'll need to look up the word in the dictionary or do a quick internet search like, "Is vice president hyphenated?" to confirm.

(Spoiler! Vice president isn't hyphenated, but vice-president-elect is!)

If a compound noun is neither combined nor hyphenated, it is open.

What If the Writing Is Unclear?

Sometimes, you'll run across a scenario in which an open compound noun makes a sentence hard to read and understand.

Take this sentence for example:

Her casual t-shirt wearing boss entered the room.

  • Is casual modifying t-shirt or boss?

It's impossible to say as written. If the shirt is what is casual, it's advisable to write casual-t-shirt-wearing boss. If the boss is casual, then casual, t-shirt-wearing boss would be appropriate.

making sense

When you understand compound nouns, it becomes easier to pluralize them.

Click through to the Got It? section for the tips and tricks you need to pluralize compound nouns with ease!

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