A compound modifier is where two or more words are used together to describe a noun, for example, an “up-to-date account”, not as individual, sequential descriptions, such as “the wide, rugged plains”.
The compound modifier takes on the role of an adjective, describing the object, and needs to be hyphenated: A “10-step process”, “blue-green algae”, “coarse-grained texture”, “two-thirds full”, “half-yearly result”, “tailor-made dress”, “do-it-yourself instructions” and “ex-footballer”.
Be careful with hyphens when you use two or more compound modifiers in sequence and drop the last word of the modifier for economy’s sake. It is correct to say: A “five- and 10-cent machine”, or “four- , five- and six-year-olds”.
The hyphen can also be used with prefixes when the root word starts with a capital letter, such as “pre-World War II, un-American, anti-Government”.
The exception to the rule which governs the hyphenation of compound modifiers is when the first word of the compound modifier is an adverb ending in “-ly”, such as “poorly painted wood”, “freshly decorated rooms”, “quickly growing area”.