There are some well-established permanent compound adjectives that have become solid over a longer period, especially in American usage: earsplitting, eyecatching, and downtown. However, in British usage, these, apart from downtown, are more likely written with a hyphen: ear-splitting, eye-catching. Points of the compass are generally solid: northwest, northwester, northwesterly, northwestwards, but North-West Frontier. Hyphenated compound adjectives
A compound adjective is hyphenated if the hyphen helps the reader differentiate a compound adjective from two adjacent adjectives that each independently modify the noun. Compare the following examples:
ü acetic acid solution: a bitter solution producing vinegar or acetic acid (acetic + acid + solution);
ü acetic-acid solution: a solution of acetic acid.
The hyphen is unneeded when capitalization or italicization makes grouping clear:
ü old English scholar: an old person who is English and a scholar, or an old scholar who studies English.
ü Old English scholar: a scholar of Old English.
If, however, there is no risk of ambiguities, it may be written without a hyphen: Sunday morning walk.
Hyphenated compound adjectives may have been formed originally by an adjective preceding a noun: round table → round-table discussion; blue sky → blue-sky law, red light → red-light district, four wheels → four-wheel drive (the singular, not the plural, is used).
Others may have originated with a verb preceding an adjective or adverb: feel good → feel-good factor, buy now, pay later → buy-now pay-later purchase.
Yet others are created with an original verb preceding a preposition: stick on → stick-on label, walk on → walk-on part, stand by → stand-by fare, roll on, roll off → roll-on roll-off ferry.
The following compound adjectives are always hyphenated when they are not written as one word:
Ø An adjective preceding a noun to which -d or -ed has been added as a past-participle construction, used before a noun: loud-mouthed hooligan, middle-aged lady, rose-tinted glasses.
Ø A noun, adjective, or adverb preceding a present participle: an awe-inspiring personality, a long-lasting affair, a far-reaching decision.
Ø With numbers spelled out or as numerics in initial position: seven-year itch, five-sided polygon, 20th-century poem, 30-piece band, tenth-story window.
Ø Compound adjectives with high- or low-: high-level discussion, low-price markup.
Ø Colours in compounds: a dark-blue sweater, a reddish-orange dress.
Ø Fractions as modifiers are hyphenated: five-eighth inches, but if numerator or denominator are already hyphenated, the fraction itself does not take a hyphen: a thirty-three thousandth part.
Ø Fractions used as nouns have no hyphens: I ate only one third of the pie.
Ø Comparatives and superlatives in compound adjectives also take hyphens: the highest-placed competitor, a shorter-term loan.
Ø However, a construction with most is not hyphenated: the most respected member.
Ø Compounds including two geographical modifiers: Afro-Cuban, African-American (sometimes), Anglo-Asian. ButCentral American.
The following compound adjectives are not normally hyphenated:
Ø Where there is no risk of ambiguity: a Sunday morning walk.
Ø Left-hand components of a compound adjective that end in -ly that modify right-hand components that are past participles (ending in -ed): a hotly disputed subject, a greatly improved scheme, a distantly related celebrity.
Ø Compound adjectives that include comparatives and superlatives with more, most, less or least: a more recent development, the most respected member, a less opportune moment, the least expected event.
Ø Ordinarily hyphenated compounds with intensifying adverbs in front of adjectives: very much admired classicist, really well accepted proposal.
Compound Verbs
From a morphological point of view, some compound verbs are difficult to analyze because several derivations are plausible. Blacklist, for instance, might be analyzed as an Adjective + Verb compound, or as an Adjective + Noun compound that becomes a verb through zero derivation. Most compound verbs originally have the collective meaning of both components, but some of them later gain additional meanings that may predominate the original, accurate sense. Therefore, sometimes the resultant meanings are seemingly barely related to the original contributors.
Compound verbs composed of a noun and verb are comparatively rare, and the noun is generally not the direct object of the verb. In English, compounds such as *bread-bake or *car-drive do not exist. Yet we find literal action words, such as breastfeed, taperecord and washing instructions on clothing as for example hand wash.
Here are the most common patterns of compound verb derivation: