A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Compounds and words formed with prefixes - Compounds used as adjectives
Spelling
Part III. Style 20 spelling

It is difficult to predict when a compound word, or a compound modifier, should be hyphenated, left open (with a space, not a hyphen, between elements), or closed (spelled as one word). The best authority is your dictionary. If you cannot find a compound there, follow the principles in the following paragraphs to decide whether or not to hyphenate. If you cannot find the form in either place, leave the compound open.

The patterns outlined below are not hard-and-fast rules. You will have to decide many individual cases on the basis of context, personal taste, or common usage in your discipline. Although much of the suggested hyphenation is logical and aids readability, some is only traditional.

20.3.1 Compounds used as adjectives

Some compounds are used only as adjectives. In most cases, hyphenate such a compound when it precedes the noun it modifies; otherwise leave it open.

Before noun

open-ended question

full-length treatment

duty-free goods

thought-provoking commentary

over-the-counter drug

a frequently referred-to book

spelled-out numbers

After noun

most of the questions were open ended

treatment is full length

goods brought in duty free

commentary was thought provoking

drug sold over the counter

this book is frequently referred to

numbers that are spelled out

There are a few exceptions:

If a compound that would normally be hyphenated is preceded and modified by an adverb (such as very), omit the hyphen, because the grouping of the words will be clear to the reader.

Before noun with modifier

a well-known author

an ill-advised step

After noun with modifier

a very well known author

a somewhat ill advised step

Hyphenate compounds that begin with all and cross, except for a few words that are conventionally closed, such as crossover (check your dictionary when in doubt).

Before noun

all-encompassing treatment

After noun

text that includes cross-references

Close up compounds that end with the terms borne, like, and wide, unless the first part of the compound has three or more syllables, is a proper noun, or ends with the same letter with which the second term begins.

General pattern

foodborne

childlike

worldwide

Exceptions

mosquito-borne

bell-like

Chicago-wide

Comparative constructions beginning with such terms as more/most, less/ least, and better/best should be hyphenated only when there may be confusion about whether the comparative term is modifying the adjective that follows within the compound or the noun after the compound.

Modifying adjective

colleges produce more-skilled

workers

Modifying noun

we hired more skilled

for the workers holidays

Constructions that consist of an adverb ending in -ly followed by an adjective are not compounds and should not be hyphenated in any context.

Before noun

highly developed species

widely disseminated literature

After noun

the species was highly developed

literature has been widely disseminated