Theoritical aspects

Compound word is a productive way of Word-Formation
A compound word is a combination of two or more words that function as a single unit of meaning. When two (or more) elements which could potentially be used as stems are combined to form another stem, the form is said to be a compound. A compound lexeme (or simply a compound) can thus be defined as a lexeme containing two or more potential stems, Since each potential stem contains at least one root, a compound must contain at least two roots.( If one of the potential stems that makes up the compound is itself compound, the resultant form may, of course, contain more than two roots, paint-box.)
However, this definition is not quite sufficient, since derivational process may at times apply to forms containing more than one root (e.g. school-master, super-highway). In such cases it is said that the base of the derivational process is compound, but not that the whole lexeme is a compound. A compound may therefore be more fully defined as a lexeme containing two or more potential stems that has not subsequently been subjected to a derivational process. It should be noted that while derivation may apply to forms containing more than one root, the presence of two roots is not criteria for derivation as it is for compounding.
It is frequently useful to have a term to cover both the forms produced by compounding to contrast these with forms produced by inflection and words which are made up of just roots.
There are three types of compounds: those are written as single words, with no hyphenation, are called closed compounds the word “flowerpot”, for example. Hyphenated compounds, such as “merry-go-round” and “well-being”, are the second type. Those in the third group, called open compounds, are written as separate words – the nouns “school bus” and “decision making”.
Keep in mind that compounds can function as different parts of speech. In such cases, the type of compound “carryover” as a noun and an adjective:
The money from that line item will carry over to next year`s budget.
The money we used for the trip was part of the carryover from last year`s budget.
Carryover funds can be used to cover a deficit.
When you don`t know in which category a particular compound belongs, first try looking it up in the dictionary. You will see there that some compounds are hyphenated regardless of their function in a sentence. For example, “on-site” is a hyphenated compound when it functions as an adjective or as an adverb: “The team conducted on-site visits” and “The team conducted its review on-site”.
The real confusion begins when the compound is not given in the dictionary. That is, it is a compound that is being formed for a very specific situation. In such cases, we have rely on guidelines provide by the style manual to which we adhere. Our style manual of choice, the Chicago Manual of Style, has a lengthy section devoted to compound words- evidence that the rules are not simple.
One way to decide if a hyphen is necessary is to see if the phrase might be ambiguous without it. For example, “large-print paper” might be unclear written as “large print paper” because the reader might combine “print” and “paper” as a single idea rather than combining “large” and “print”. Another such example is “English-language learners”. Without the hyphens, a reader might think we are talking about English people who are learning any language rather than people who are learners of the English language.
On the other hand, no one is going to be confused by the phrase “chocolate chip cookies” or “Saturday morning cartoons”. In other words, the open compounds (i.e., no hyphen) “chocolate chip” and “Saturday morning” are so well known that there is no room for ambiguity. The open compound “high school” is so common, for another example, that we would not hyphenate the high phrase “high school students”. We would, however, hyphenate “high risk” in phrase “high risk students”.
The other time we must use hyphenation is to join a word to past participle to create a single adjective preceding the noun it modifies: “a well-intentioned plan”, or “a horseshoe-shaped bar”. Be aware, however, that we do not hyphenate these same phrases when they follow the nouns they modify:
This is a government-mandated program.
The program is government mandated.
She is a well-respected student.
She is well respected as a teacher.
Another basic rule is that we never hyphenate compounds that are created with “-ly” adverbs, even when they precede the nouns they modify: “a fully developed plan”, or “a nationally certified teacher”. Here are more examples:
We sent heavily fortified troops.
The troops were heavily fortified.
All newly employed nurses must be evaluated regularly.
All the nurses on the eight floors are newly employed.
Compound words are two words put together. Knowing when to use a hyphen and when to spell them as one word is difficult. British & U.S. usages do not always agree, and different dictionaries published in the same country do not always agree. In U.S. usage, fewer hyphens are than in British usage. Many more compound words are written as one word today than were written that way in past. Compound adjectives are two separate words that together modify a noun. They are usually written with a hyphen if they come before the word they modify, but sometimes usage changes and they become one word.
Written as written with written as two
One word words a hyphen separate
Firsthand first-degree first aid
Stream boat engine post-Victorian land office
Postgraduate meridium post-mortem stream
In English, words, particularly adjectives and nouns, are combined into compound structures in a variety of ways. And once they are formed, they sometimes metamorphose over time. A common pattern is that two words- fire fly, say- will be joined by a hyphen for a time- fire-fly- and then be joined into one word – firefly. In this respect, a language like German, in which words are happily and immediately linked one to the other, might seem to have an advantage. There is only one sure way to know how to spell compounds in English; use an authoritative dictionary.
There are three forms of compound words:
1. the closed form, in which the words are melded together, such is firefly, secondhand, softball, childlike, cross-town, redhead, keyboard, makeup, notebook;
2. the hyphenated form such is daughter-in-law, master-at-arms, over –the-counter, six-pack, six-years-old, mass-produced;
3. the open form, such as post office, real estate, middle class, full moon, half sister attorney general.
How are words modified by an adjective – “a little school.” “The yellow butter”- is different from a compound word-“a high school”, “the peanut butter”- is a nice and philosophical question. In clearly has something to do with the degree to which preceding word changes the essential character of the noun, the degree to which the modifier and the noun is separable. If you were diagramming a sentence with a compound word, you would probably keep the words together, on the same horizontal line.
Modifying compounds are often hyphenated to avoid confusion. The New York Public Library`s Writers Guide points out than an old-furniture salesman clearly deals in old furniture, but an old furniture salesman would be an old man. We probably would not have the same ambiguity, however, about a car used dealer. When compounded modifiers precede a noun, they are often hyphenated: part-time teacher, fifty-yard wide field, fire-resistant curtains, and high –speed chase. When those same modifying words came after the noun, however, they are not hyphenated: a field fifty yard wide, curtains that are fire resistant, etc. the second-rate opera company gave a performance that was first rate. Comparative and superlative forms of adjectives are hyphenated when compounded with other modifiers: a highly rated bank, a partially refunded ticket, publicly held securities. Sometimes hyphenated modifiers lost their hyphens when they become compound nouns: A clear decision-making process was evident in their decision making. The bluish was very slowly disappearing from the bluish grey- sky. This is not always s, however: your high- rise apartment building is also known as a high-rise.When modifying a person with his or her age, the compounded phrase is hyphenated: my six-years-old son. However, when the age comes after the person, we don`t use a hyphen. My son is six years old. He is, however, a six-years-old.