When You Should Hyphenate, Open, or Close a Compound Word
And why getting compounds right matters
The concept of compound words is simple to understand, but using compound words correctly can sometimes prove challenging to writers. The trick is to understand how a term is being used — as a noun, a compound adjective that precedes the noun it modifies, a compound adjective that follows the noun it modifies, or a verb. Then you can determine how the term should be written.
Common compound words
But first, let’s consider some common compound words. Simply put, compound words are formed when two or more separate words are combined. The first type of compound words taught to very young students are closed (with no space or hyphen), as in airplane, birthday, campfire, daydream, earlobe, firefly, etc. The next most common are open but are still considered compound words: ice cream, high school, dry cleaning. And then there are hyphenated compound words that always take hyphens: sister-in-law, merry-go-round, self-esteem.
All the examples of compound words listed above are nouns. But two of the open compound words, “ice cream” and “high school,” are commonly used as adjectives as well, as in “ice cream social” and “high school student.” Even though in each of these examples an open compound word…