Compound Nouns

In English grammar, a compound noun (or nominal compound) is a construction made up of two or more nouns that function as a single noun. With somewhat arbitrary spelling rules, compound nouns can be written as separate words like tomato juice, as words linked by hyphens like sister-in-law or as one word like schoolteacher.

A compound noun whose form no longer clearly reveals its origin, such as bonfire or marshall, is sometimes called an amalgamated compound; many place names (or toponyms) are amalgamated compounds — for example, Norwich is the combination of "north" and "village" while Sussex is a combination of "south" and "Saxons."

One interesting aspect of most compounds nouns is that one of the origin words is syntactically dominant. This word, called the headword, grounds the word as a noun, such as the word "chair" in the compound noun "easychair."

The Function of Compound Nouns

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What Are Compound Words in English?

By Richard Nordquist

Creating a compound noun, or compounding inherently changes the meaning of the parts of the new word, typically as a result of their tandem usage. Take for instance again the word "easychair" wherein the adjective "easy" describes a noun as being without difficulty or being comfortable and "chair" means a place to sit — the combined new word would mean a comfortable, hassle-free place to sit. 

In this example, too, the form of the word easy changes from an adjective to a noun, based on the part of speech the headword (chair) functions as. This means that unlike an adjective-plus-noun phrase, a compound noun serves a different function and meaning altogether in a sentence.

James J. Hurford uses the compound noun tractor driver as compared to the adjective-plus-noun phrase careless driver to emphasize the difference between the two usages in "Grammar: A Students Guide." A careless driver, he states, "is both careless and a driver, while a tractor driver is a driver but certainly not a tractor!"

Special Rules of Usage

As Ronald Carter and Michael McCarthy put it in "Cambridge Grammar of English," the compound noun structure is "extremely varied in the types of meaning relations it can indicate," from what the object is for like waste-paper basket to what something is made of like woodpile or metal slab, how something works like a convection oven to what someone does like a language teacher.

As a result, usage rules for everything from punctuation to capitalization can be confusing, especially for new English grammar learners. Fortunately, there are a few set guidelines for common questions related to these syntactical problems.

For example, the possessive form of compound nouns, as Stewart Clark and Graham Pointon describe in "The Routledge Student Guide to English Usage," must always place the apostrophe possessive after "the whole of a compound noun, even if the last word is not the head word of the phrase: The Mayor of London's dog (the dog belongs to the Mayor, not London)."

In terms of capitalization, the principle of bicapitalization applies to most compound noun forms. Even in Clark and Pointon's example, both Mayor and London are capitalized in the compound noun because the phrase itself is a proper compound noun.