2. A compound adjective is a group of words that provides a single description of a noun that follows. Use hyphens between the words to make the words appear as a single unit. Thus, proper hyphenation of compound adjectives increases understanding and speeds the reader along.
• The Small Business Administration approved a small-business loan for $2 million.
• He said that the large-appliance industry has been weakened by the recent economic depression.
• His "better-late-than-never" attitude kept him from hearing the opening remarks of many meetings.
Each compound adjective in these sentences provides a single description of the noun that follows it, regardless of whether the adjective has two, three, or more words in it. The decision to place a hyphen between two words or to leave the hyphen out will often have a significant effect on the meaning of a sentence.
• We need more qualified workers. (We need what? Great numbers of qualified workers.)
• We need more-qualified workers. (We need what? Workers who are more qualified than the workers we have now.)
• The large appliance industry is suffering. (Which industry? The appliance industry, which is large.)
• The large-appliance industry is suffering. (Which industry? The industry that produces large appliances.)
Hyphenated compound adjectives are used only before nouns. When they come after nouns, they are not hyphenated.
• The up-to-date report was submitted on time. (comes before the noun)
• The report was up to date. (comes after the noun)
• It was a well-written report. (comes before the noun)
• The report was well written. (comes after the noun)
A compound word is a combination of two or more words used to express a single concept. Consistency in the treatment of compounds is always difficult. There are wide variations in acceptable style, and the rules that do exist sometimes conflict or overlap. More important than absolute consistency in the formation of compounds is the union or separation of the elements so that terms can be easily read, understood, and pronounced.
- A compound noun or adjective consisting of a short verb plus a word that normally functions as a preposition or an adverb is usually solid, unless a hyphen is needed for readability.
- It is preferable to spell out the name of a chemical compound (lowercase) in text the first time it is used. Subsequently, the chemical symbols can be used, especially in equations and formulas.
- An isotope of an element that is designated by its chemical symbol should be written with the mass number displayed as a superscript preceding the symbol.
use of 238U for fuel
the shipping of 60C
An isotope written out in text is lowercase and is followed by a hyphen and the mass number written on the baseline.
- Hyphenate words and abbreviations that form a compound adjective immediately preceding a noun, particularly if one element is a past or present participle or if meaning or readability is enhanced.
real-time power system applications
well-known Chexal-Lellouche correlation method
- Hyphenate compound adjectives containing units of measure and time.
a 24-ft (7.3-m) room
1-in.-(2.54-cm) diameter pipe
a 3-m pole
a 600-MW plant
- If a compound adjective does not contain a past or present participle, if there is no chance of misreading it, or if the adjective contains a symbol ($,°C, %), no hyphen is necessary.
fossil fuel plant
$20 million budget
air quality standards
an 800°C metal temperature
low energy rate
- Do not hyphenate compound adjectives formed from scientific terms (e.g., chemical, disease, and plant names) unless a hyphen appears in their noun form.
carbon dioxide gas
methyl bromide mixture
sodium chloride solution
prickly pear cactus
whooping cough vaccine
equivalent uranium content
But: hydrogen-oxygen reaction (to differentiate two elements versus one chemical compound)
- In almost all cases, hyphenate high- and low- adjectival compounds.
But: lower energy rates
high coal prices
low level waste (see Style Guide for other exceptions due to industry standards)
- Hyphenate a compound adjective formed by an adverb plus an adjective or participle, especially if the adverb can be misread to modify the noun following the compound.
If the adverb ends in -ly, the compound is open.
roughly equivalent amounts
thoroughly tested materials
- Omit the hyphen if a compound adjective is preceded by an adverb that modifies only the first word of the compound.
a well-equipped plant
a very well equipped plant
- A compound adjective that follows the noun is ordinarily not hyphenated unless it is shown with a hyphen in the dictionary.
That plant is best equipped for the job.
Their energy policy was ill-advised.
- A compound adjective whose second element is a letter or a numeral is usually not hyphenated.
Phase 1 results
Type 304 stainless steel
- A compound adjective that is a foreign language phrase is not hyphenated unless it is hyphenated in the original language.
per diem rate
in situ experiment
- With compound adjectives that drop a repeated element, the hyphen is retained to indicate parallel relationships. This guideline also holds true for adjectives formed with prefixes or suffixes.
diamond- or rotary-drill rig
long-, mid-, or short-range plans
30- to 40-year plant life
pre- and post-1995 data
However, if the last adjective or a prefix is ordinarily solid, it remains so.
surface- and groundwater studies
mono- and polycellular materials>
pre- and postcombustion cycles
- A slash is used to indicate alternatives, to separate the numerator and denominator in numerical fractions, to designate certain electrochemical notation, and with the phrase "and/or." It does not replace a hyphen or a dash.
high-heat and/or high-speed applications
ac/dc transmission lines
3/4-in. (1.9-cm) steel pipe
Prefixes and Suffixes
- A word combined with a prefix is ordinarily solid (one word), even if the combination results in a double vowel.
- Hyphens are used to set prefixes and suffixes off from proper nouns, proper adjectives, and numerals.
- A hyphen is used to distinguish between words with the same spelling but different meanings and to prevent misreading, mispronunciation, or visual confusion.
re-treat (to treat again)
re-fuse (to fuse again)
- A hyphen is used with a prefix that applied to a two-word hyphenated compound and with a prefix that is doubled.
- A hyphen is used to connect a prefix and an open compound.
pre-Civil War days
post-industrial revolution technology