A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007
Compounds used as both nouns and adjectives
Spelling
Part III. Style 20 spelling
Some compounds are primarily nouns but can also function as adjectives when they precede and modify another noun. (Unlike the examples in 20.3.1, these compounds are rarely used as adjectives after a noun, and then only with a verb such as was or are, as in the third example below.) In most cases, hyphenate such a compound when it precedes a noun that it modifies; otherwise leave it open.
Adjective before noun
the decision-making process
a continuing-education course
a middle-class neighborhood
Noun, or adjective after noun
decision making became her specialty
a program of continuing education
her neighborhood was middle class
There are a few exceptions:
For a compound that begins with e (short for electronic), ex, or self, use a hyphen in all contexts. One exception: if self is preceded by un, the compound should be closed (as in unselfconscious).
ex-husband
self-destructive
e-mail
For a compound that ends with elect, use a hyphen in all contexts when the name of the office is only one word, but leave it open when the name is two or more words.
president-elect
district attorney elect
For a compound formed by two coordinated nouns that could be joined by and, use a hyphen in all contexts.
actor-singer
mother-daughter relationship
city-state
parent-teacher conference
For a compound composed of directional words, use a closed compound when the term describes a single direction. Use a hyphen if the compound consists of coordinated nouns that could be joined with and or by.
northeast
a street running north-south
southwest
east-southeast winds
Compounds that describe family relationships vary in whether they are closed up or hyphenated. When in doubt, consult your dictionary. (For the plural and possessive forms of in-law compounds, see 20.1.2 and 20.2.2, respectively.)
grandfather
stepdaughter
great-grandmother
son-in-law
Some familiar phrases are always hyphenated.
stick-in-the-mud
jack-of-all-trades
COMPOUNDS INCLUDING PROPER NOUNS. Leave open most compounds that include proper nouns, including names of ethnic groups.
Adjective before noun
African American culture
French Canadian explorer
Middle Eastern geography
State Department employees
Korean War veterans
Noun, or adjective after noun
an African American has written
the explorer was French Canadian
the geography of the Middle East
employed by the State Department
veterans of the Korean War
If, however, the first term is shortened, use a hyphen.
Afro-American culture
an Afro-American has written
If coordinated terms could be joined by and, hyphenate them.
Israel-Egypt peace treaty
Spanish-English dictionary
COMPOUNDS INCLUDING NUMBERS. If a compound includes a number, hyphenate it if it precedes a noun that it modifies; otherwise leave it open. (For the use of numerals versus spelled-out numbers, see chapter 23.)
Adjective before noun
fifty-year project
four-year-old child
twentieth-century literature
third-floor apartment
214-day standoff
Noun, or adjective after noun
the project took fifty years
the child was four years old
studied the literature of the twentieth century
she lived on the third floor
standoff that lasted 214 days
There are a few exceptions:
Always leave open a compound including the word percent, and give the number in arabic numerals (see 23.1.3).
a 15 percent increase
increased by 15 percent
Always use a hyphen to spell a fraction with words. (See 23.1.3 for use of numerals versus spelled-out numbers in fractions.)
a two-thirds majority
a majority of two-thirds
For a fraction beginning with half or quarter, use a hyphen when it precedes a noun that it modifies; otherwise leave it open.
Adjective before noun
a half-hour session
a quarter-mile run
Noun, or adjective after noun
after a half hour had passed
ran a quarter mile
For a compound indicating a span of numbers, use a hyphen in both terms, but omit the second part of the compound in the first term.
five- to ten-minute intervals
eight- to ten-year-olds