HYPHEN

A compound adjective should be hyphenated before a noun (unless the compound itself carries a modifier) but not following it unless subject to misreading or hyphenated in Webster's as an adjective: a well-respected man; a very well respected man; a man well respected for his bravery; he is well respected for his bravery; quick-witted retort; the retort was quick-witted; a two-ton truck; a jet-pack-powered stroll; but an old stone wall (the stone wall is old).

a. After an adverb that ends in -ly, do not hyphenate unless ambiguity results:

nearly dead hopes
 newly set aside parklands

b. Some adverbs do not end in -ly.  Of these, compound modifiers with the following are generally hyphenated before nouns: dead, long, near, and well (well-dressed man, near-dead hopes). Unless the meaning is ambiguous or a compound is hyphenated in Webster's, do not hyphenate compound modifiers with almost, already, best, early, ever, last, late, less, more, most, much, never, not, now, once, only, seldom, sometimes, still, very, yet.  See even.Consult Webster's, especially for compounds with over and under.

c. Compound modifiers containing cardinal numbers are hyphenated before nouns when the compound contains a unit of measurement or spelled out number:

a two-dollar tie
 an eight-foot pole, but eight feet of pole
 a 13½-year-old; 11- to 14-year-old children; 11- and 14-year-olds; 11-through-14-year-olds
 an 11½-by-4½-foot box, but 11½ by 4½ feet
 a three-by-four-foot box, but three by four feet
 a 35-millimeter slide; 35-mm slide or 35mm slide
 a three-by-five card or a three-by-five
 a four-by-four or 4WD or FWD or 4x4 are all acceptable for a four-wheel-drive vehicle

d. With more than one compound modifier distinguish between several possibilities and an inclusive range:

Two- to three-day forecasts are now possible.
 A two-to-three-day forecast would help him plan.
 Snow will be in the 10-to-14-inch range.

e. A compound with an ordinal, a comparative, or a superlative is not hyphenated except to prevent ambiguity or if in Webster's:

fifth largest city
 farthest reaching trade
 the best known person
 the first ever race
 second-growth timber
 third-ranked convention city
 best-selling novel
 faster than normal ship

f. Do not hyphenate between capitalized words that are an entity, with certain exceptions. Hyphenate when required by Webster's, after a prefix, or when the hyphen is necessary for sense. If one element in a compound modifier is itself a compound, an en dash may be used in place of a hyphen:

Holy Week ceremonies
 New York skyline
 Latin American countries
 Los Angeles–oriented view
 South American countries
 French-Canadian restaurant
 proto-Aryan roots
 pre-Columbian vase
 color TV series
 third-century B.C. head
 New-York Historical Society
 Scotch-Irish descent

g. Chemical terms used as adjectives are not hyphenated except if ambiguous and when used with the mass number: carbon dioxide test, but carbon-14 dating; iron-oxide red; strontium-90, strontium-90 fallout, Sr-90 fallout.

h. Dates:  A hyphen means up to and including when used between dates: November 15-21; 1941-45. When using from, do not use a hyphen but spell out to or through and give complete date: from 1941 through 1945. With hyphen use only the last two digits except where three zeros would come together or decades are different: 1962-65, 1900-1901, 1900-1910, 1949-1950, 1941-1963. Never use one digit alone in a date: 1947-49 not 1947-9.

i. Foreign terms used as adjectives are not hyphenated:

ex post facto laws, per capita income, status quo regime, but laissez-faire policy.

j. A compound modifier in which the second word is possessive is not hyphenated:

park ranger's job, magazine researcher's inquiry, but bird's-eye view, snail's-pace walk.

k. A compound modifier within quotes is not hyphenated unless the compound is hyphenated in Webster's:

a "one man" attempt, "Azores high" cliffs, a "pigeon-toed" table.

l. The punctuation can influence the meaning: red, white, and blue flags (solid-colored flags), red-white-and-blue flags (tricolors). Do not hyphenate compound color modifiers unless both elements are colors of equal value: blue-black sky, gray-green eyes, but bluish black sky, lemon yellow dress, jade green lake, cobalt blue dish, dark blue suit, white sand beaches. To avoid ambiguity, note: light-blue suit (color), light blue suit (weight). Note the difference between an old-brick home and an old brick home, depending on whether the bricks or the home is old.

m. Compound nouns appearing in Webster's and widely used do not need to be hyphenated when used as adjectives unless ambiguous. For example: polar bear, sea turtle, foreign exchange, income tax, real estate, fossil fuel.

n. Dual-heritage designations are not hyphenated as a noun or adjective: African American, Mexican American, French Canadian. 

o. Use an en dash instead of a hyphen in a compound modifier when one or both of the elements is itself a compound: Civil War–era firearms, first-class–second-class rivalries. Sometimes it is clearer to hyphenate the entire term: cold-weather-related deaths, natural-gas-fired power plants.

See also ADJECTIVES AND ADVERBS, PUNCTUATION OF, COMMA, and DIVISION OF WORDS.