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The Plural of Compound Nouns


How to form the plural of compound nouns

Plural of compound nouns

Forming the plural of compound nouns might be confusing for some. Before presenting some quick tips to form these compounds, let's review what compound nouns are first.

Compound Nouns

A compound noun is a noun made up of two or more words (e.g. toothpaste, haircut or daughter-in-law). Most compound nouns can be formed as follows:

Forms Examples
noun + noun train station
noun + adjective handful
adjective + noun blackberry
full moon
verb (ing) + noun breakwater
swimming pool
noun + verb (ing) haircut
skydiving
verb + preposition check-in
noun + preposition passer-by
preposition + noun underground
noun + preposition + noun father-in-law

As you can see from the examples above, some compound nouns are spelled as one word (e.g. handful), but others with hyphens (e.g. father-in-law) or separated by a space (e.g. full moon).

Forming the plural of compound nouns

The plurals of compound nouns are generally formed by adding 's' to the principal word (i.e. the most significant word in the compound), also called the head of the compound. The head informs us about what the compound refers to. The other elements of the compound modify the head and are called the head's dependents.

Examples:

compounds head plural
car park park car parks
blackboard board blackboards
mother-in-law mother mothers-in-law
taxi driver driver taxi drivers

Compound nouns with -ful

Compound nouns with '-ful' (e.g. truckful, handful) may have two possible plurals. The 's' can be added either t:o

  • the head noun (e.g. trucksful, handsful)
  • or to '-ful ' (e.g. truckfuls, handfuls).

It is just a question of consistency.

More examples:

Compound nouns with '-ful' Plural
handful handsful handfuls
mouthful mouthsful mouthfuls
spoonful spoonsful spoonfuls
bucketful bucketsful bucketfuls
cupful cupsful cupfuls
truckful trucksful truckfuls

Compound nouns ending in a preposition

When the compound is formed with a noun and a preposition, (e.g. passer-by), the plural is formed by adding an 's' to the noun.

Examples:

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

When neither element of a compound is a noun, the plural is formed by adding 's' to the last word. For example, the compound noun 'grown-up' is made of the word 'grown', which is the past participle of the verb 'grow', and the preposition 'up'. The plural of 'grown-up' is formed by adding 's' to 'up' (i.e. 'grown-ups).

More examples:

Compound Noun Plural
grown-up grown-ups
go-between go-betweens
check-in check-ins
higher-up higher-ups
also-ran also-rans

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