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, also known as karmadharaya compounds, 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, the 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 also known as tatpurusha compounds.

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 or bahuvrihi compound, the semantic head is not explicitly expressed. A redhead, for example, is not a kind of head, but is a person with a red head. 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 someone who is barefoot is not a foot -- they're someone with a foot that is bare. And, outside of veterinary surgery, a lionheart is not a type of heart, but a person with a heart like a lion (in its bravery, courage, fearlessness, etc.).

Note in general the way to tell the two apart:

Can you paraphrase the meaning of the compound "[X . Y]" to A person/thing that is a Y, or ... that does Y, if Y is a verb (with X having some unspecified connection)? This is an endocentric compound.
Can you paraphrase the meaning if the compound "[X . Y]" to A person/thing that is with Y, with X having some unspecified connection? This is an exocentric compound.
Exocentric compounds occur more often in adjectives than nouns. A barefoot girl, for example, is not a girl that is a bare foot, but a girl with a bare foot. Similarly, 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, esp. -ed. Hence, 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 car-carrier is a clear endocentric determinative compound: it is a thing that is a carrier of cars. The related adjective, car-carrying, is also endocentric: it refers to an object which is a carrying-thing (or equivalent, 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-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 bubbe-maise that butterflies are petite 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).