Compound words are inseparable vocabulary units that are structurally and semantically based on the relationship between their components through which they are motivated. There are two types of relationship between the components of a compound generally recognized in linguistic literature:
that of coordination and subordination and accordingly compound words may be classified into coordinative (often termed copulative) and subordinative (often termed determinative).
a) coordinative compounds
In coordinative compounds neither of the components dominates the other, both are structurally and semantically independent and constitute two structural and semantic centres as insecretary-stenographer, actor-manager, bittersweet, etc. The constituent stems in these compounds belong to the same part of speech and most often to the same semantic group. Coordinative compounds distinguish three groups:
a) the so-calledadditive compounds that best represent coordinative compound words, e.g.queen-bee, actor-manager.They denote a person or an object that is two things at the same time; thus, e.g.secretary-stenographer is a person who is both a stenographer and a secretary;actor-manager is an actor and a manager at the same time.
b)reduplicative compounds which are the result of the repetition of the same stem as ingoody-goody, fifty-fifty, hush-hush, pooh-pooh, tick-tick.
c) compounds formed by joiningthe phonically variated rhythmic forms of the same stem which either alliterate with the same initial consonant but vary the vowels, e.g.drip-drop, sing-song, ding-dong, or rime by varying the initial consonants, e.g.walkie-talkie, clap-trap, willy-nilly, pell-mell, helter-skelter. Words of this subgroup are often termed pseudo-compounds and some linguists consider them irrelevant to productive word-formation owing to the doubtful morphemic status of their components. In most cases the constituent members of these words, when substracted from them do not present stems of independently functioning words, carry no lexical meaning of their own and are mere rime combinations of fanciful, meaningless sound-clusters.
Coordinative compounds of the last two groups (reduplicated and riming words) are mostly restricted to the colloquial layer and are characterized by a heavy emotive charge.
b) subordinative compounds.
In subordinative compounds the components are neither structurally nor semantically equal in importance but are based on the domination of one component over the other. The second component in these words is the structural centre, the grammatically dominant part of the word, which imparts its part-of-speech meaning to the whole word and refers it to a certain lexico-grammatical class, as instone-deaf, agelong which are obviously adjectives,wrist-watch, baby-sitter, road-building which are nouns.
It must be mentioned that though a distinction between coordinative and subordinative compounds can generally be made, there is no hard and fast borderline between them. On the contrary, the borderline, and this is especially true of additive coordinative compounds, is rather vague and transitions are greatly fluctuating. It often happens that one and the same compound may with equal right be interpreted either way-as a coordinative or a subordinative compound, e.g.woman-doctor may be understood as 'a woman who is at the same time a doctor';clock-tower-'a tower that at the same time serves as a clock' or there can be traced a difference of importance between the components-a woman-doctoris primarily felt to be'a doctor who happens to be a woman'; a clock-tower-'a tower with a clock fitted in';mother-gooseis primarily understood as'a goose, who is a mother', etc.; thus the relations between the components tend to be understood as relations of apposition, i.e. relations of subordination. Coordinative compounds make a comparatively small group of words whereas the bulk of Modern English compound words belong to subordinative words, so in our further treatment we shall confine ourselves to the description of subordinative compounds.