A compound word (compound) is a combination of two or more words used together to convey a new meaning. Compounds can be open (rat race), closed (sunset), or hyphenated (in-depth).
Compound words are often born with a hyphen. Some evolve into open compounds (ice-cream is now ice cream), others become closed (e-mail is now email), and the odd one remains hyphenated (mother-in-law). Many compounds add or drop hyphens depending on their function in a sentence. And, the same word can be treated every which way depending on the dictionary you check. It’s no wonder compounds cause confusion.
Let’s take a look at how to treat different types of compound words.
A compound adjective is a combination of two or more words that work together to modify a noun. Use a hyphen when a compound adjective comes before a noun (bad-news story), not after (He’s bad news).
If, however, a compound isn’t listed in the dictionary and contains one of the following terms, it should be hyphenated either before or after the noun it modifies.
fold, with numerals (100-fold) or spelled-out numbers that are hyphenated (thirty-three-fold)
free, when it’s the second element in a compound (debt-free)
odd (100-odd songs, a hundred-odd words)
self (self-satisfying), except when followed by a suffix (selfish) or preceded by un (unselfish)
style (decorated Victorian-style, 1960s-style furniture)
Note: Do not hyphenate the adverb very (very lucky mother) or adverbs ending in ly (wonderfully gifted daughter). It is already obvious that these adverbs modify the adjective or participle that follows them.
A compound noun is a combination of two or more words that function together as a noun. Compound nouns are rarely hyphenated, but there are exceptions (voice-over, mother-of-pearl, Jack-of-all-trades).
If a compound noun isn’t listed in the dictionary, leave it open; however, if it contains one of the following terms, the Chicago Manual of Style recommends adding a hyphen.
elect (president-elect), except with an open compound (vice president elect)
in-law (mother-in-law, parents-in-law)
old (a two-year-old)
self (self-esteem), except when followed by a suffix (selfishness) or preceded by un (unselfishness)
step, with grand (step-granddaughter) and great (step-great-granddaughter)
A compound verb is combination of two or more words that act as a verb. There are phrasal verbs, prepositional verbs, verbs with auxiliaries, and single-word compound verbs. Only single-word compound verbs may be hyphenated (bottle-feed), but they can also be closed (breastfeed) or open (work out). According to the Chicago Manual of Style, if the compound isn’t listed, leave it open.
Always hyphenate nouns with equal but separate functions (writer-editor, city-state).
Combining forms are word elements used only in compounds or derivatives. Whereas affixes must be added to root words, combining forms can be used with affixes or other combining forms. Compounds formed with combining forms are usually closed if permanent and hyphenated if temporary. If you don’t see the compound in the dictionary, use a hyphen (agro-social, quasi-journalistic).
Directions and compass points
When three directions are combined, use a hyphen after the first (west-southwest).
The Copyeditor’s Handbook lists two rules for hyphenating spelled-out fractions:
- Place a hyphen between the numerator and denominator (one-third, three and one-half).
- Omit the hyphen between the numerator and denominator if either component is already hyphenated (seventy-five hundredths).
Hyphenate forms such as four-thirty when they come before a noun (four-thirty bus).
The hyphen: If in doubt, leave it out
The hyphen isn’t winning any popularity contests. According to YourDictionary.com, “American English discourages the use of hyphens where there is no compelling reason.” Even the Brits, who tend to be more liberal with the hyphen, are using it less these days. In the 2007 edition of the Shorter Oxford English Dictionary, about 1600 hyphens were eliminated from compound words.
The Chicago Manual of Style prefers a “spare hyphenation style,” and offers the advice: “When in doubt, opt for an open compound.” If the compound cannot be found in the dictionary and the terms are not listed in the manual, “hyphens should be added only if doing so will prevent a misreading or otherwise significantly aid comprehension.”
Clarity is key
If compounds still confuse you, don’t worry. With so many types of compound words—and different rules for each—you can’t be expected to keep track. That’s why you should always check the dictionary for compounds—and stick to the same dictionary for consistency’s sake. If the word isn’t listed, follow these guidelines. If you’re still in doubt, leave it open—unless a hyphen is needed for clarity. Your number one priority, after all, is making your writing as clear and easy to read as possible.