The term unit means one of the elements into which a whole may be divided or analysed and which possesses the basic properties of thiswhole. The units of a vocabulary or lexical units are two-facet elements possessing form and meaning. The basic unit forming the bulk of the vocabulary is the word. Other units are morphemes that is parts of words, into which words may be analysed, and set expressions or groups of words into which words may be combined.

The treatment of words in lexicology cannot be divorced from the study of all the other elements in the language system to which words belong. It should be always borne in mind that in reality, in the actual process of communication, all these elements are interdependent and stand in definite relations to one another. We separate them for convenience of study, and yet to separate them for analysis is pointless, unless we are afterwards able to put them back together to achieve a synthesis and see their interdependence and development in the language system as a whole.

The importance of English lexicology is based not on the size of its vocabulary, however big it is, but on the fact that at present it is the world’s most widely used language. One of the most fundamental works on the English language of the present — "A Grammar of Contemporary English” by R. Quirk, S. Greenbaum, G. Leech and J. Svartvik (1978) — gives the following data: it is spoken as a native language by nearly three hundred million people in Britain, the United States, Ireland, Australia, Canada, New Zealand, South Africa and some other countries. The knowledge of English is widely spread geographically — it is in fact used in all continents. It is also spoken in many countries as a second language and used in official and business activities there. This is the case in India, Pakistan and many other former British colonies. English is also one of the working languages of the United Nations and the universal language of international aviation. More than a half world’s scientific literature is published in English and 60% of the world’s radio broadcasts are in English. For all these reasons it is widely studied all over the world as a foreign language.

Lexicology (from Gr lexis ‘word’ and logos ‘learning’) is the part of linguistics dealing with the vocabulary of the language and the properties of words as the main units of language. The term v o c a b u l a-r y is used to denote the system formed by the sum total of all the words and word equivalents that the language possesses. The term word denotes the basic unit of a given language resulting from the association of a particular meaning with a particular group of sounds capable of a particular grammatical employment. A word therefore is simultaneously a semantic, grammatical and phonological unit.