A compound is a word composed of more than one free morpheme.Adams, §3.1. The English language, like many others, uses compounds frequently. English compounds may be classified in several ways, such as the word classes or the semantic relationship of their components.
History
English inherits the ability to form compounds from its parent the Proto-Indo-European language and expands on it.Fortson, §682. Close to two-thirds of the words in the Old English poem Beowulf are found to be compounds.Meyer, p. 179. Of all the types of word-formation in English, compounding is said to be the most productive.Plag, §6.1.
Compound nouns Most English compound nouns are noun phrases (i.e. nominal phrases) that include a noun modified by adjectives or noun adjuncts. Due to the English tendency toward conversion, the two classes are not always easily distinguished. Most English compound nouns that consist of more than two words can be constructed recursively by combining two words at a time. Combining "science" and "fiction", and then combining the resulting compound with "writer", for example, can construct the compound "science fiction writer" or "science-fiction writer". Some compounds, such as salt and pepper or mother-of-pearl, cannot be constructed in this way, however.
Orthography: open, hyphenated, or solid (closed up) English uses many open compound nouns, a large subclass of which, by convention in accepted English orthography, are not closed up (not solidified) and are sometimes optionally hyphenated in attributive position (that is, when functioning as a noun adjunct). Examples are high school, kidney disease, and file format. Although some other languages would close up these nouns' components (for example, German usually does so), English has a tendency whereby it closes up only certain ones, usually only ones in which the head noun is monosyllabic (and even within that category, only sometimes, and in a way that is not fully standardized). For example, data set and dataset, or file name and filename, are accepted alternative forms, but file format, data format, and data analysis, which have multisyllabic heads (format and analysis), can only be spelled as open in accepted English orthography. This pattern holds for countless nouns with few exceptions. For the class with monosyllabic heads, there is a tendency that "compounds tend to solidify as they age," which is how a term such as data set becomes dataset, pin-up becomes pinup, coal mine becomes coalmine, bottle cap becomes bottlecap, and so on. Such alternative forms usually continue to coexist in accepted use; style guides often convene on preferred dictionaries as a way of achieving consistency, by declaring that the headword form there will be the default styling for each such term.
Types of compound nouns
Native English compound Since English is a mostly analytic language, unlike most other Germanic languages, it creates compounds by concatenating words without case markers.
+ Examples by word class Modifier Head Compound noun noun football adjective noun blackboard verb noun breakwater preposition noun underworld noun adjective waterproof adjective adjective bittersweet verb adverb drive-through preposition adjective over-ripe noun verb nosebleed adjective verb shortcoming verb verb buy-bust preposition verb undercut noun preposition love-in adverb preposition once-over verb adverb takeout preposition adverb forever
Most noun-verb compounds denoting people are of the form noun + verb + -er, where the noun is the object of the verb, for example fire-fighter. However, there are a few dozen common verb-object compounds – mostly dating from the 16th century and mostly with negative connotations – which have the opposite French order and which do not have a suffix -er. These have been labeled cutthroat compounds because 'cutthroat' is a typical example.see wiktionary:Category:English exocentric verb-noun compounds
As in other Germanic languages, the compounds may be arbitrarily long. However, this is obscured by the fact that the written representation of long compounds always contains spaces. Short compounds may be written in three different forms, which do not correspond to different pronunciations, though:
The or form usually consisting of newer combinations or longer words, such as "distance learning", "player piano", "ice cream". The form in which two or more words are connected by a hyphen. The following types of compounds are often hyphenated: Compounds that contain affixes: "house-build(er)" and "single-mind(ed)(ness)", Adjective–adjective compounds: "blue-green", Verb–verb compounds: "lend-lease", Compounds that contain articles, prepositions or conjunctions: "rent-a-cop", "mother-of-pearl" and "hide-and-seek". The or form in which two usually moderately short words appear together as one. Solid compounds most likely consist of short (monosyllabic) units that often have been established in the language for a long time. Examples are "housewife", "lawsuit", "wallpaper", "basketball".
Usage in the US and in the UK differs and often depends on the individual choice of the writer rather than on a hard-and-fast rule; therefore, spaced, hyphenated, and solid forms may be encountered for the same compound noun, such as the triplets place name/place-name/placename and particle board/particle-board/particleboard.
Neo-classical compound
In addition to this native English compounding, there is the neo-classical type, which consists of words derived from Classical Latin, as horticulture, and those of Ancient Greek origin, such as photography, the components of which are in bound form (connected by connecting vowels, which are most often -i- and -o- in Classical Latin and Ancient Greek respectively) and cannot stand alone.Adams, §3.2.
Analyzability (transparency) In general, the meaning of a compound noun is a specialization of the meaning of its head. The modifier limits the meaning of the head. This is most obvious in descriptive compounds (known as karmadharaya compounds in the Sanskrit tradition), in which the modifier is used in an attributive or appositional manner. A blackboard is a particular kind of board, which is (generally) black, for instance.
In determinative compounds, however, the relationship is not attributive. For example, a footstool is not a particular type of stool that is like a foot. Rather, it is a stool for one's foot or feet. (It can be used for sitting on, but that is not its primary purpose.) In a similar manner, an office manager is the manager of an office, an armchair is a chair with arms, and a raincoat is a coat against the rain. These relationships, which are expressed by prepositions in English, would be expressed by grammatical case in other languages. (Compounds of this type are known as tatpurusha in the Sanskrit tradition.)
Both of the above types of compounds are called endocentric compounds because the semantic head is contained within the compound itself—a blackboard is a type of board, for example, and a footstool is a type of stool.
However, in another common type of compound, the exocentric (known as a bahuvrihi compound in the Sanskrit tradition), the semantic head is not explicitly expressed. A redhead, for example, is not a kind of head, but is a person with red hair. Similarly, a blockhead is also not a head, but a person with a head that is as hard and unreceptive as a block (i.e. stupid). And a lionheart is not a type of heart, but a person with a heart like a lion (in its bravery, courage, fearlessness, etc.).
There is a general way to tell the two apart. In a compound "[X . Y]":
Can one substitute Y with a noun that is a Y, or a verb that does Y? This is an endocentric compound. Can one substitute Y with a noun that is with Y? This is an exocentric compound.
Exocentric compounds occur more often in adjectives than nouns. A V-8 car is a car with a V-8 engine rather than a car that is a V-8, and a twenty-five-dollar car is a car with a worth of $25, not a car that is $25. The compounds shown here are bare, but more commonly, a suffixal morpheme is added, such as -ed: a two-legged person is a person with two legs, and this is exocentric.
On the other hand, endocentric adjectives are also frequently formed, using the suffixal morphemes -ing or -er/or. A people-carrier is a clear endocentric determinative compound: it is a thing that is a carrier of people. The related adjective, car-carrying, is also endocentric: it refers to an object which is a carrying-thing (or equivalently, which does carry).
These types account for most compound nouns, but there are other, rarer types as well. Coordinative, copulative or dvandva compounds combine elements with a similar meaning, and the compound meaning may be a generalization instead of a specialization. Bosnia-Herzegovina, for example, is the combined area of Bosnia and Herzegovina, but a fighter-bomber is an aircraft that is both a fighter and a bomber. Iterative or amredita compounds repeat a single element, to express repetition or as an emphasis. Day by day and go-go are examples of this type of compound, which has more than one head.
Analyzability may be further limited by cranberry morphemes and semantic changes. For instance, the word butterfly, commonly thought to be a metathesis for flutter by, which the bugs do, is actually based on an old wives' tale that butterflies are small witches that steal butter from window sills. Cranberry is a part translation from Low German, which is why we cannot recognize the element cran (from the Low German kraan or kroon, "crane"). The ladybird or ladybug was named after the Christian expression "our Lady, the Virgin Mary".
In the case of verb+noun compounds, the noun may be either the subject or the object of the verb. In playboy, for example, the noun is the subject of the verb (the boy plays), whereas it is the object in callgirl (someone calls the girl).
Sound patterns Stress patterns may distinguish a compound word from a noun phrase consisting of the same component words. For example, a black board, adjective plus noun, is any board that is black, and has equal stress on both elements. The compound blackboard, on the other hand, though it may have started out historically as black board, now is stressed on only the first element, black. Thus a compound such as the White House normally has a falling intonation which a phrase such as a white house does not.
Compound modifiers
English compound modifiers are constructed in a very similar way to the compound noun. Blackboard Jungle, leftover ingredients, gunmetal sheen, and green monkey disease are only a few examples.
A compound modifier is a sequence of modifiers of a noun that function as a single unit. It consists of two or more words (adjectives, gerunds, or nouns) of which the left-hand component modifies the right-hand one, as in "the dark-green dress": dark modifies the green that modifies dress.
Solid compound modifiers There are some well-established permanent compound modifiers 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.
Other solid compound modifiers are for example: Numbers that are spelled out and have the suffix -fold added: "fifteenfold", "sixfold". Points of the compass: northwest, northwestern, northwesterly, northwestwards. In British usage, the hyphenated and open versions are more common: north-western, north-westerly, north west, north-westwards.
Hyphenated compound modifiers