Forming Plurals of Compound Nouns

Pluralizing Compound Nouns

Here are the rules for pluralizing the different types of compound nouns. This infographic summarizes how to pluralize a compound noun:

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(Rule 1) Forming the Plurals of Hyphenated Compound Nouns

When a compound noun is hyphenated, add "s" to the principal word. (In these examples, the principal words are in bold.)

Compound Noun	Plural
brother-in-law	brothers-in-law
passer-by	passers-by
water-bottle	water-bottles

Beware the Exception! There is one notable exception to this rule. If the compound noun consists of a verb and preposition (see Rule 8), add "s" to the end.

Compound Noun	Plural
love-in	love-ins

Read more about compound noun with hyphens.

(Rule 2) Forming the Plurals of Multi-Word Compound Nouns

When a compound noun consists of two or more words, add "s" to the principal word. (In these examples, the principal words are in bold.)

Compound Noun	Plural
Knight Templar	Knights Templar
bus stop	bus stops
full moon	full moons

(Rule 3) Forming the Plurals of Compound Nouns without a Principal Noun

If there is no principal word, follow the usual rules for forming a plural, which usually means adding "s" to the end of the word.

Compound Noun	Plural
forget-me-not	forget-me-nots
court-martial	court-martials*

* "Courts martial" is also an acceptable plural of "court martial." This version is used by those who deem "court" to be the principal word.

(Rule 4) Forming the Plurals of Single-Word Compound Nouns

When the compound noun is a single word, follow the usual rules for forming a plural (i.e., pluralize the ending).

Compound Noun	Plural
breakwater	breakwaters
rainforest	rainforests
seagrass	seagrasses

(Rule 5) Forming the Plurals of Terms in the Form [Word] "of" [Word]

With a term in the form [word] of [word] (e.g., "cup of tea"), the first word is always the principal word. Form the plural by pluralizing the first word.
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Compound Noun	Plural
cup of tea	cups of tea
man of war	men of war
right of passage	rights of passage

(Rule 6) Forming the Plurals of Compound Nouns Ending "Ful"

When a compound noun in the form [container]-"ful", by far the safest option is to add an "s" to the end to form the plural. However, it might be acceptable to add an "s" to the first half of the compound.
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Compound Noun	Plural
bucketful	bucketfuls
cupful	cupfuls
handful	handfuls
mouthful	mouthfuls
spoonful	spoonfuls
truckful	truckfuls

Many native English speakers feel that "bucketsful" sounds more natural than "bucketfuls." If you are a native English speaker, you can follow whichever version sounds more natural to you. However, if you use two or more of these terms in the same document, you should strive for consistency.

Unsure? If you're unsure, add "s" to the end. Sorted.

More technical help? If you're still unsure which version to choose (e.g., "mouthsful" or "mouthfuls"), use Google's Ngram viewer (which searches millions of books for the terms). This tool tells you - in less than a second - how the terms have been used over the last two centuries. Here are some examples:

• bucketsful and bucketfuls (opens a new tab)
(This example suggests both versions are acceptable.)
• mouthsful and mouthfuls (opens a new tab)
(This example suggests "mouthsful" is wrong but "mouthfuls" is correct.)
• spoonsful and spoonfuls (opens a new tab)
(This example suggests "spoonsful" used be acceptable but has been wrong for nearly a century.)

(Rule 7) Forming the Plurals of Compound Nouns with a Noun and a Preposition

When a compound noun consists of a noun and a preposition, pluralize the noun.
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In these examples, the nouns are in bold.

Compound Noun	Plural
passer-by	passers-by
hanger-on	hangers-on

(Rule 8) Forming the Plurals of Compound Nouns with a Verb and a Preposition

When a compound noun consists of a verb and a preposition, add an "s" to the end.
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In these examples, the verbs are in bold.

Compound Noun	Plural
check-in	check-ins
build-up	build-ups
take-out	take-outs
love-in	love-ins

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