A noun is a word that names a person, place, thing or abstract idea, and a compound noun is simply a noun that consists of two or more words that are either separate or joined together to form one word. Compound words are formed by joining a noun with another word, another noun, an adjective, a verb or a preposition. Some examples of common compound nouns are ‘swimming pool’, ‘haircut’, ‘football’, ‘washing machine’, ‘bus stop’ and ‘toothbrush’.
Compound nouns are used in three different forms. The first is the open or spaced form, in which the words that make up the compound noun are separated. Examples include ‘orange juice’, ‘post office’ and ‘light year’. The second form of compound nouns is words that are hyphenated. These include ‘jack-in-the-box’, ‘attorney-at-law’ and ‘go-between’. The last form is called closed or solid and consists of compound nouns that are written as a single word, such as ‘bedroom’, ‘flashlight’ and ‘butterfly’.
CORRECT: The zebra decided that he needed to go to the veterinarian for a check-up when he noticed that he was losing his stripes.
INCORRECT: The zebra decided that he needed to go to the veterinarian for a checkup when he noticed that he was losing his stripes.
Pluralizing compound nouns usually entails adding -s or -es to the end of the base word or head, which is the principal word in the compound noun. Therefore, bedroom becomes bedrooms, matchbox becomes matchboxes and passerby becomes passersby. Hyphenated compounds follow the same rule but the base word is not necessarily the last word. For example, mother-in-law becomes mothers-in-law because ‘mother’ is the primary word in the noun. The same applies to attorney-at-law, which becomes attorneys-at-law. Likewise, open form compounds are sometimes pluralized by adding -s or -es to the first word, as in attorneys general and courts martial. There are also a few compound nouns that can have two heads, such as manservant and city-state. In the former case, the first word of the compound noun, ‘man,’ has an irregular plural form. When this happens, both parts of the compound noun are pluralized. Therefore, manservant becomes menservants. In the latter case, the first part of the word, ‘city’ has a standard plural form so only the last word is pluralized, making city-states the plural of city-state.
CORRECT: When the zebra noticed that he wasn’t wearing any underclothes beneath his stripes, he hoped that he wouldn’t be spotted by any passers-by.
INCORRECT: When the zebra noticed that he wasn’t wearing any underclothes beneath his stripes, he hoped that he wouldn’t be spotted by any passer-bys.