A Practical and Authoritative Guide to Contemporary English. 1996.
Page 256
Compound modifiers formed of capitalized words should not be hyphenated: Old English poetry, Iron Age manufacture, New World plants.
1
Usage is divided with regard to compounds that are proper names used to designate ethnic groups. Under normal circumstances such terms when used as nouns or adjectives should appear without a hyphen: a group of African Americans, many Native Americans, French Canadians in Boston, a Jewish American organization, an Italian American neighborhood, Latin American countries. However, many (but not all) compounds of this type are now frequently hyphenated: African-Americans, Asian-American families, French-Canadian music but Native American myths.
2
Nouns or adjectives consisting of a short verb combined with a preposition are either hyphenated or written solid depending on current usage. The same words used as a verb are written separately: a breakup but break up a fight; a bang-up job but bang up the car.
3
Two nouns of equal value are hyphenated when the person or thing is considered to have the characteristics of both nouns: secretary-treasurer, city-state, time-motion study.
4
Compound forms must reflect meaning. Consequently, some compounds may change in form depending on how they are used: Anyone may go but Any one of these will do; Everyone is here but Every one of these is good.
5
Scientific compounds are usually not hyphenated: carbon monoxide poisoning, dichromic acid solution.
6
Phrases
Phrases used as modifiers are normally hyphenated: a happy-go-lucky person, a here-today-gone-tomorrow attitude.
7
A foreign phrase used as a modifier is not hyphenated: a bona fide offer, a per diem allowance.
8
Numbers
Numbers from twenty-one to ninety-nine and adjective compounds with a numerical first element (whether spelled out or written in figures) are hyphenated: twenty-one, thirty-first, second-rate movie, third-story window, three-dimensional figure, six-sided polygon, ten-thousand-year-old bones, 13-piece band, 19th-century novel, decades-old newspapers.
