GrammarPhile Blog

No aspect of style causes greater difficulty than compound adjectives. When a compound adjective is shown hyphenated in the dictionary, you can assume only that the expression is hyphenated when it occurs directly before a noun. When the same combination of words falls elsewhere in the sentence, the use or omission of hyphens depends on how the words are used.

Adjective + Noun

Hyphenate an adjective and a noun when these elements serve as a compound modifier before a noun. Do not hyphenate these elements when they play a normal role elsewhere in the sentence (for example, as the object of a preposition or of a verb). However, if the expression continues to function as a compound adjective, retain the hyphen.

• high-speed printers; these printers run at high speed
• a plain-paper fax; the fax uses plain paper
• red-carpet treatment; roll out the red carpet
• a part-time job; the job is part-time (compound adjective)
• a long-term investment in bonds; the investment runs for a long term; but: the investment is long-term (compound adjective)
• a larger-size shirt; the shirt is a larger size
• the finest-quality goods; the goods are of the finest quality

Compound with Number or Letter

When a number and a noun form a one-thought modifier before a noun (as in six-story building), make the noun singular and hyphenate the expression. When the expression has a normal form and a normal function elsewhere in the sentence, do not hyphenate it.

• a one-way street; a street that runs only one way
• a first-person account; a story written in the first person
• a first-rate job; a job that deserves the first (or highest) rating; but: a job that is first-rate
• a two-piece suit; a suit consisting of two pieces
• a 20-year mortgage; a mortgage running for 20 years
• a 55-mile-an-hour speed limit; a speed limit of 55 miles an hour
• 24-hour-a-day service; service 24 hours a day
• an 8-foot ceiling; a ceiling 8 feet above the floor
  
  Exceptions: a 15 percent decline; a $4 million profit; a twofold increase, but: a 12-fold increase; a secondhand car, but: a second-degree burn

A hyphenated compound adjective and an unhyphenated possessive expression often provide alternative ways of expressing the same thought. Do not use both styles together.

• a one-year extension, or a one year's extension, but not: a one-year's extension
• a two-week vacation, or a two weeks' vacation, but not: a two-week's vacation

More examples:

• he does A-plus (or A+) work; a grade of A plus (or A+)
• in A1 condition; but A.1. steak sauce